Part 15

FIG. 104.—SKELETON OF DISTAL PART OF LEFT HIND LIMB OF OX, INTERNAL VIEW. _24_, Tuber calcis; _25_, large metatarsal bone; _30_, first phalanx; _31_, second phalanx; _32_, third phalanx. (After Ellenberger-Baum, Anat. für Künstler.) ]

The =small metatarsal= bone is a quadrilateral disc a little less than an inch in width and height. Its anterior face bears a facet for articulation with the large metatarsal bone.

The large metatarsal bone is usually regarded as consisting of the fused third and fourth metatarsal bones. The medullary cavity is subdivided like that of the large metacarpal bone. Some anatomists, however, consider that the ridges at the upper end of each border represent the second and fifth metatarsals (Rosenberg and Retterer). On this basis the small bone would be the first metatarsal.

The =phalanges= and =sesamoids= resemble those of the thoracic limb so closely as to render separate description unnecessary.

SKELETON OF THE PIG

VERTEBRAL COLUMN

The =vertebral formula= is C_{7}T_{14–15}L_{6–7}S_{4}Cy_{20–23}.

[Illustration:

FIG. 105.—SKELETON OF PIG, LATERAL VIEW.

_a_, Cranium; _b_, upper jaw; _c_, lower jaw; _1H.-7H._, cervical vertebræ; _1R.w._, first thoracic vertebra; _13 R.w._, thirteenth thoracic vertebra (next to last); _1L._, first lumbar vertebra; _6L._, sixth lumbar vertebra (next to last usually); _K._, sacrum; _S._, coccygeal vertebra; _1R._, first rib; _14R._, last rib; _R.kn._, costal cartilages; _St._, sternum; _d_, supraspinous fossa of scapula; _d′_, infraspinous fossa; _1_, spine of scapula; _2_, neck of scapula; _e_, humerus; _3_, head of humerus; _4_, tuberosities of humerus; _5_, deltoid tuberosity; _6_, external epicondyle of humerus; _f_, radius; _g_, ulna; _7_, olecranon; _h_, carpus; _18–25_, carpal bones; _i-i⁗_, metacarpus; _k-k⁗_, proximal phalanges; _l-l⁗_, middle phalanges; _m-m⁗_, distal phalanges; _n_, _o_, sesamoids; _p_, ilium; _8_, external angle of ilium (tuber coxæ); _9_, internal angle of ilium (tuber sacrale); _10_, superior ischiatic spine; _q_, ischium; _11_, tuber ischii; _r_, pubis; _12_, acetabulum; _s_, femur; _13_, trochanter major; _14_, trochanter minor; _15_, external epicondyle; _t_, patella; _u_, tibia; _16_, crest of tibia; _17_, external condyle of tibia; _v_, fibula; _w_, tarsus; _26–31_, tarsal bones; _26′_, tuber calcis. (After Ellenberger, in Leisering’s Atlas.) ]

The =cervical vertebræ= are short and wide. The bodies are elliptical in cross-section, the long diameter being transverse. The anterior articular surfaces are slightly convex from side to side and concave dorso-ventrally; the posterior ones are slightly concave. A ventral crest is not present. The arches are wide from side to side, but the laminæ are narrow, so that a considerable interval (Spatium interarcuale) separates adjacent arches dorsally. The pedicles are perforated by a foramen on either side in addition to the usual intervertebral foramina. The transverse processes divide into two branches, both of which increase in size from the third to the sixth. The upper branch projects outward and backward; it is short and is thickened at its free end. The lower branch is a quadrilateral plate directed ventrally; each overlaps the succeeding one to a small extent, and the series forms the lateral boundary of a deep and wide groove beneath the bodies. The spines increase in height from the third to the last; the anterior ones are inclined backward, the posterior ones forward. The last cervical is recognized by the great length of its spine (ca. 10 cm. in the adult), the absence of the ventral plate of the transverse process, and the flatness of the body, which bears a pair of small facets on its posterior margin for the heads of the first ribs. It has foramina transversaria, and usually two foramina in either side of the arch.

The dorsal arch of the =atlas= bears a large tuberosity. The ventral tubercle is long, compressed laterally, and projects back under the axis. The wing is flattened and bears a posterior tuberosity. The foramen transversarium passes through the posterior border of the wing to the fossa under the latter, and is not visible dorsally; it is sometimes very small or absent. The sides of the vertebral foramen bear two lateral projections which partially divide it into a ventral narrow part, which receives the odontoid process, and a dorsal larger part for the spinal cord. In the fresh state the division is completed by the transverse ligament, which is attached to the projections.

The =axis= has a large spinous process, which is directed upward and backward. The odontoid process is a thick cylindrical rod. The transverse process is very small and the foramen transversarium is often incomplete.

[Illustration:

FIG. 106.—ATLAS OF PIG, DORSAL VIEW.

_a_, Wing; _b_, ventral tubercle; _c_, foramen transversarium; _d_, alar foramen; _e_, intervertebral foramen; _f_, dorsal tuberosity; _g_, articular surface corresponding to that of posterior articular process of typical vertebra; _h_, facet on ventral arch for odontoid process. (Ellenberger-Baum, Anat. d. Haustiere.) ]

[Illustration:

FIG. 107.—AXIS OF PIG, LEFT LATERAL VIEW.

_a_, Odontoid process (dens); _b_, spinous process; _c_, anterior articular process; _d_, posterior articular processes; _e_, transverse process; _f_, foramen transversarium; _g_, bar of bone which bounds _h_, intervertebral foramen; _i_, vertebral foramen. (Ellenberger-Baum, Anat. d. Haustiere.) ]

The =thoracic vertebræ= are often fifteen in number. Their bodies are relatively long, constricted in the middle, and without ventral crests. Their extremities are elliptical, depressed in the middle and prominent at the periphery. The arch is perforated by a foramen on either side, and in most of the series there is also a foramen in the posterior part of the root of the transverse process which communicates with the former or with the posterior intervertebral foramen. Sometimes there is a foramen in the anterior part of the process also. There are mammillary processes except on the first two; in the posterior five or six vertebræ they project from the anterior articular processes. The facet for the tubercle of the rib is absent or fused with that for the head in the last five or six. The last transverse process is lumbar in character, plate-like, and about an inch (2 cm.) long. Small accessory processes occur in the posterior part of the region. The first spinous process is broad, very high, and inclined a little forward. The others diminish very gradually in length to the tenth, beyond which they are about equal. The second to the ninth are inclined backward, the tenth is vertical (anticlinal), and the rest incline forward. The width decreases decidedly from the fourth to the tenth, beyond which there is a gradual increase. The summits are slightly enlarged and lie almost in a straight line.

The occurrence of fifteen thoracic vertebræ appears to be quite common, and some observers have recorded the existence of sixteen and even seventeen; a reduction to thirteen is rare.

The =lumbar vertebræ= are six or seven in number. The bodies are longer than in the thoracic region and bear a ventral crest. They become wider and flatter in the posterior part of the series. The arches are deeply notched, and are separated by an increasing space dorsally. The mammillary processes project outward and backward. The transverse processes are bent downward and incline a little forward. Their length increases to the fifth and is much diminished in the last. They form no articulation with each other or with the sacrum. The posterior edge of the root of the process is marked by a notch in the anterior part of the series, a foramen in the posterior part. The spines are broad and incline forward, with the exception of the last, which is narrow and vertical.

Lesbre states that six and seven lumbar vertebræ occur with almost equal frequency. The number may be reduced to five, and the number of presacral vertebræ varies from twenty-six to twenty-nine.

The =sacrum= consists usually of four vertebræ, which fuse later and less completely than in the other domesticated animals. It is less curved than in the ox. The spines are absent, excepting small rudiments on the last two segments. The middle of the dorsal surface is flattened and smooth, and presents openings into the sacral canal between adjacent arches (Spatia interarcualia). On either side are the superior sacral foramina, and tubercles which indicate the fused articular processes. The wings resemble those of the ox. The anterior articular processes are very large. The pelvic surface resembles that of the ox, but is not so strongly curved, and the transverse lines are very distinct.

[Illustration:

FIG. 108.—SACRUM OF PIG, DORSAL VIEW.

_a_, Wing; _b_, dorsal sacral foramina; _c_, articular process; _1–4_, segments or sacral vertebræ. (Ellenberger-Baum, Anat. d. Haustiere.) ]

The =coccygeal vertebræ= are specially characterized by the presence of functional articular processes on the first four or five, beyond which these processes become non-articular and smaller. The arches of the first five or six are complete. The transverse processes are broad and plate-like in the anterior part of the series and diminish very gradually.

The numerical variation here is twenty to twenty-six according to the observation of several anatomists. Lesbre states that he has found twenty-three most frequently.

=Curves.=—The cervical region is practically straight. The thoracic and lumbar regions form a gentle curve, concave ventrally, the highest point of which is at the junction of the two regions. The sacral promontory is not so pronounced as in the ox, and the sacral curve is flatter.

THE RIBS

The =ribs= number fourteen or fifteen pairs, of which seven are sternal and seven or eight asternal usually. They are in general strongly curved in the improved breeds, so that there is a fairly distinct angle, except toward the end of the series. The backward slope of the posterior ribs is slight. The first rib is prismatic, has a large sternal end, and a very short cartilage. The width is greatest in the third to the sixth, and the length in the sixth and seventh usually. The tuberosity fuses with the head on the last five or six. The second to the fifth form diarthrodial joints with their cartilages, which are wide and plate-like.

THE STERNUM

The =sternum= consists of six segments and resembles that of the ox in general form. The first segment (Manubrium) is long, flattened laterally, and bears a blunt-pointed cartilage on its anterior end; its posterior end forms a diarthrodial joint with the body. The latter is flattened, wide in its middle, narrow at either end. The widest segments are formed of two lateral parts, which are not completely fused in the adult. The last segment has a long narrow part which bears the xiphoid cartilage.

The =thorax= is long and is more barrel-shaped than in the horse or ox, since the ribs are more strongly curved and differ less in relative length.

[Illustration:

FIG. 109.—SKULL OF PIG, LATERAL VIEW WITHOUT MANDIBLE.

_1_, Occipital condyle; _2_, paramastoid or styloid process; _3_, bulla ossea; _4_, external auditory meatus, _5_, zygomatic process of temporal bone; _6_, sphenoid bone; _7_, orbital opening of supraorbital canal; _8_, malar bone; _9_, pterygoid bone; _10_, pterygoid process of sphenoid; _11_, pterygoid process of palate bone; _I1–3_, incisor teeth; _C_, canine tooth; _P1–4_, premolars; _M1–3_, molars. ]

BONES OF THE SKULL

CRANIUM

The =occipital bone= has an extensive squamous part or supraoccipital, which forms a very broad and prominent crest. The latter is concave, and is thick and rough above, where it forms the highest part of the skull; laterally it becomes thinner, turns downward, and is continuous with the temporal crest. Two divergent ridges pass upward from the foramen magnum, and the surface between them is concave and smooth. The greater part of the inner (or anterior) surface of the supraoccipital is united with the parietal bones, but a lower concave area faces into the cranial cavity. The foramen magnum is almost triangular, and is narrow above, where it is flanked by two small tuberosities. The paramastoid processes are extremely long and project almost straight downward. The hypoglossal foramen is at the inner side of the root of the process. The basilar part is short and wide; its lower surface bears a thin median ridge and two lateral imprints or tubercles which converge at the junction with the sphenoid bone.

[Illustration:

FIG. 110.—SKULL OF PIG, DORSAL VIEW. ]

The =interparietal= fuses before birth with the occipital. The tentorium osseum is absent.

The =parietal= is overlapped by the occipital bone behind and concurs in the formation of the occipital crest. Its external surface is divided by the parietal crest into two parts. The inner part (Planum parietale) faces upward and forward, and is flattened and smooth. Its inner border is short and straight and unites early with the opposite bone. Its anterior border is concave and joins the frontal bone. The outer part (Planum temporale) faces outward and is more extensive; it is concave, forms a large part of the temporal fossa, and is overlapped below by the squamous temporal. The parietal crest extends in a curve from the occipital crest forward and outward to the supraorbital process. The internal surface is concave and is marked by digital impressions. The lower border projects into the cranial cavity and forms a crest which separates the cerebral and cerebellar compartments laterally. The interior forms part of the frontal sinus in the adult. There is no parieto-temporal canal.

The =frontal bone= is long. The frontal surface slopes downward and forward, the inclination varying in different subjects. The anterior part is concave and is marked by the supraorbital foramen and the groove leading forward from the foramen to the nasal bone. The supraorbital canal opens into the orbit at the upper part of the inner wall of the latter. The supraorbital process is short and blunt-pointed, and is not connected with the zygomatic arch. The gap in the orbital margin is closed by the orbital ligament in the fresh state. The orbital part is extensive and forms the greater part of the inner wall of the orbit. Its upper part is perforated by the orbital orifice of the supraorbital canal, in front of which is the distinct fovea trochlearis. The ethmoidal or internal orbital foramen is situated in the lower part near the junction with the orbital wing of the sphenoid. The temporal part is very narrow and is separated from the orbital plate by a ridge which joins the pterygoid crest below. The interior of the bone is excavated by the frontal sinus in practically its entire extent in the adult. In the young subject the cavity is confined to the anterior part and the rest of the bone is thick.

The =temporal bone= has a general resemblance to that of the ox. The zygomatic process is short and stout and is bent at a right angle. The upper border of the process is thin; traced from before backward it curves sharply upward and forms a high prominence in front of the external auditory meatus; beyond this it drops rather abruptly and is then continued upward to the occipital crest. The anterior part of the lower border joins the zygomatic process of the malar, which is deeply notched. The condyle is concave in the transverse direction. The postglenoid process is absent, but the articular surface is bounded behind and internally by a crest. There is no parieto-temporal canal. The external auditory canal is very long and is directed upward and outward. The bulla ossea is large, compressed laterally, and bears a pointed muscular process in front. A narrow space intervenes between the bulla and the basilar part of the occipital bone, so that the foramen lacerum resembles that of the horse. The small hyoid process is situated in a deep depression in front of the root of the paramastoid process, and the stylo-mastoid foramen is immediately external to it. The petrous part presents no important differential features. The squamous part (including the root of the zygomatic process) contains an air-cavity, which is continuous with the sphenoidal sinus.

[Illustration:

FIG. 111.—BASAL SURFACE OF SKULL OF YOUNG PIG, WITHOUT THE MANDIBLE.

_Sq.o._, Supraoccipital; _E.o._, exoccipital; _B.o._, basioccipital; _B.s._, body of sphenoid; _Sq._, squamous temporal bone; _V_, vomer; _Mx._, maxilla; _Pa._, horizontal part of palate bone; _P.p._, palate process of maxilla; _Z_, malar bone; _J_, premaxilla; _D.c._, canine tooth; _J1–3_, incisor teeth; _O_, temporal fossa; _1_, occipital crest; _2_, for. magnum; _3_, occipital condyle; _4_, paramastoid (styloid) process; _5_, bulla ossea; _6_, for. lacerum basis cranii; _7_, pterygoid process of sphenoid; _8_, posterior nares; _9_, anterior palatine foramen; _10_, palatine cleft. (Struska, Anat. d. Haustiere.) ]

The =sphenoid bone= is short and resembles that of the ox in general. The body is narrow. The pituitary fossa is very deep, and is limited behind by a prominent dorsum sellæ; the dorsum bears lateral projections, the =posterior clinoid processes=. The foramen ovale is absent, being included in the foramen lacerum anterius. The other foramina are like those of the ox. The pterygoid process is broad and twisted. Its base is not perforated and its free edge is thin and sharp. It concurs with the pterygoid and palate bones in the formation of the pterygoid fossa, which opens backward and is not present in the horse or ox. The sphenoidal sinus is very large and occupies the body, the temporal wings, and a great part of the pterygoid processes in the adult; it is continued into the temporal bone as mentioned above.

The =ethmoid bone= has a relatively long perpendicular plate, which is marked by ridges corresponding to the ethmoidal meatuses. The cribriform plate is extensive and very oblique, so that it and the crista galli are almost in line with the basi-cranial axis. A linear series of relatively large foramina is found on either side of the crista. The lateral mass consists of five endoturbinals and eighteen ectoturbinals (Paulli). The lamina papyracea concurs in the formation of the pterygo-palatine fossa.

FACE

The =maxilla= is extensive. Its external surface forms a longitudinal groove, which is continued upon the premaxilla in front and the facial parts of the lacrimal and malar behind. The infraorbital foramen—sometimes double—is large and is situated above the third or fourth cheek tooth. The alveolus for the canine tooth produces a ridge at the anterior end which is very pronounced in the boar. The facial crest extends forward from the root of the zygomatic process and fades out behind the infraorbital foramen; in some specimens it is prominent and thin-edged, in others it is rounded and projects little. The zygomatic process is short but stout and buttress-like; it is overlapped externally by the malar. The maxillary tuberosity forms in the young subject a long bulla, which occupies most of the pterygo-palatine fossa and contains the developing permanent molars; after the eruption of the teeth the tuberosity flattens and joins the vertical part of the palate bone. The palatine process is very long and is marked in its anterior part by transverse ridges corresponding with those of the mucous membrane of the palate. The anterior palatine foramen is near the junction with the palate bone; from it the palatine groove can be traced distinctly along the entire length of the process. The alveolar border presents a large alveolus for the canine tooth at its anterior end; behind this are seven alveoli for the cheek teeth, which increase in size from first to last. The maxillary foramen and infraorbital canal are very large. The maxillary sinus is small.

The body of the =premaxilla= is narrow and prismatic. It presents three alveoli for the incisor teeth, which are separated by short intervals and diminish in size from before backward. As in the ox, a narrow space separates the right and left bones and takes the place of the foramen incisivum. The palatine process is long and narrow. The nasal process is very extensive and is somewhat rhomboid in outline. Its upper border forms a very long suture with the nasal bone, and the lower articulates to about the same extent with the maxilla. The palatine fissure is relatively wide.

The horizontal part of the =palate bone= forms a fourth to a fifth of the length of the palate; its palatine surface is triangular, the apex being anterior; its nasal surface is deeply grooved and smooth. A pterygoid process (processus pyramidalis of man) projects backward and downward, and its thick rounded end is received between the pterygoid process of the sphenoid and the pterygoid bone. The perpendicular part is largely overlapped externally by the maxilla and concurs in forming part of the palatine canal. Superiorly the two plates separate and inclose an air-cavity which opens into an ethmoidal meatus. The inner plate curves inward and unites with the vomer and ethmoid to form a horizontal plate (Lamina transversalis), which divides the posterior part of the nasal cavity into an upper olfactory part and a lower respiratory part.

The =pterygoid bone= is nearly vertical in direction, and is narrow in its middle, wide at each end. The external surface is free below and forms the inner wall of the pterygoid fossa. The lower end is notched and forms a distinct hamulus.

The =nasal bone= is very long and its width is almost uniform, except at the anterior end, which is pointed and reaches almost as far forward as the premaxilla. The facial surface is flattened from side to side. In profile it is nearly straight in some subjects, variably concave in others. The external border is free to a small extent in front only; otherwise it is firmly connected with the premaxilla and maxilla. In the adult the frontal sinus extends into the posterior part of the bone.

The =lacrimal bone= is very sharply bent. Its facial surface presents a deep depression, surmounted by a ridge or tubercle. On or close to the orbital margin are two lacrimal foramina which lead to the lacrimal canals. The orbital surface presents a fossa in which the inferior oblique muscle of the eyeball arises, and its lower part bears a crest, which is crossed obliquely by a vascular furrow. The upper border articulates with the frontal only. The bone concurs in the formation of the maxillary sinus.

The =malar bone= is strongly compressed from side to side. Its facial surface is small and presents a fossa which is continuous with the depressions of the maxilla and lacrimal. The orbital surface is still smaller and is smooth and deeply grooved. The zygomatic process is very extensive, especially in the vertical direction. Its external surface is convex and free, and bears a rough eminence in its middle. Its internal surface is concave; it is overlapped in front by the maxilla, and in the remainder of its extent is free and smooth. The upper border is thick and rounded in front, where it forms the lower part of the orbital margin; behind this it forms an extensive notch which receives the zygomatic process of the temporal. (It might be regarded as dividing into frontal and temporal branches.) The lower border is convex and becomes thinner behind.

The =turbinal bones= resemble those of the ox. The superior turbinal is, however, relatively longer, less fragile, and more firmly attached to the nasal bone. There is no middle turbinal.

The =vomer= is very long. The anterior extremity reaches to the body of the premaxilla or very close to it. The lower border is received into a groove formed by the nasal crest of the maxillæ and palate bones and in front by the palatine processes of the premaxillæ. The posterior border is concave, thin, and sharp.

The =os rostri= (or prenasal bone) is situated in the snout between the nostrils. It has the form of a short three-sided prism. The upper surface is convex and is notched at each end. The lateral surfaces are concave, smooth, and converge below, forming a grooved lower border. The posterior surface is triangular, notched centrally, and rough laterally. The anterior surface is deeply pitted and is surrounded by an irregular sharp border.