Part 2

1. Skeleton 2 2. Fourth Thoracic Vertebra 3 3. Fourth Thoracic Vertebra 3 4. Thoracic Vertebræ 5 5. Lumbar Vertebræ 7 6. Sacrum 9 7. Sacrum 9 8. Caudal Vertebra 11 9. Caudal Vertebra 11 10. Cervical Vertebræ 12 11. Sixth Cervical Vertebra 13 12. Atlas 13 13. Axis 15 14. Ligaments of the Odontoid Process 18 15. Rib 19 16. Sternum 20 17. Occipital Bone 22 18. Occipital Bone 22 19. Interparietal 25 20. Sphenoid 25 21. Presphenoid 29 22. Temporal 31 23. Temporal 31 24. Tympanic Bulla 33 25. Petrous Bone 34 26. Frontal 37 27. Maxillary Bone 39 28. Maxillary Bone 39 29. Premaxillary 41 30. Nasal 42 31. Ethmoid and Vomer 43 32. Ethmoid and Vomer 43 33. Palatine 45 34. Lachrymal 46 35. Malar 46 36. Mandible 48 37. Mandible 48 38. Hyoid 49 39. Skull, Dorsal Surface 50 40. Skull, Side View 53 41. Skull, Ventral Surface 55 42. Cavities of Skull 57 43. Skull, Median Section 60 44. Scapula 62 45. Scapula 62 46. Clavicle 64 47. Humerus 65 48. Humerus 65 49. Radius and Ulna 68 50. Radius and Ulna 68 51. Bones of the Hand 70 52. Ligaments of the Elbow 74 53. Ligaments of the Elbow 74 54. Innominate Bone of Kitten 76 55. Innominate Bone 77 56. Femur 79 57. Tibia and Fibula 81 58. Bones of the Foot 83 59. Calcaneus 83 60. Knee-joint 89 61. Knee-joint 89 62. Muscles of the Skin 94 63. Muscles on Dorsal Side of Head 97 64. Muscles of Face 102 65. Ventral Muscles of Thorax, Neck, and Head 109 66. Pterygoid and Palatal Muscles 112 67. Muscles of Tongue, Hyoid, and Pharynx 114 68. First Layer of Body Muscles 117 69. Deep Muscles of the Vertebræ and Ribs 125 70. Dorsal Muscles of Lumbar and Caudal Regions 127 71. Deep Muscles of Neck 135 72. Muscles on the Ventral Surface of the Cervical Vertebræ 143 73. Second Layer of Body Muscles 149 74. Diaphragm 152 75. Lateral Muscles of Arm 158 76. Origin of Lateral Muscles on Scapula 160 77. Medial Muscles of Arm 162 78. Origin of Medial Muscles on Scapula 163 79. Deep Medial Muscles of Arm 167 80. Deep Lateral Muscles of Arm 169 81. Areas of Origin of Muscles on Ventral Surface of Humerus 171 82. Areas of Origin of Muscles on Medial Side of Humerus 171 83. Areas of Origin of Muscles on Dorsal Surface of Left Humerus 171 84. Tendons on Back of Hand 175 85. Deep Muscles of Forearm 177 86. Insertions of Muscles on Radius and Ulna 178 87. Insertions of Muscles on Radius and Ulna 182 88. Mm. Lumbricales, etc. 183 89. Deep Muscles of Palm of Hand 184 90. Lateral Muscles of the Leg 192 91. Medial Muscles of the Leg 197 92. Deep Medial Muscles of Thigh 200 93. Teeth of the Upper Jaw 225 94. Teeth of the Lower Jaw 226 95. Tongue, Epiglottis, etc. 227 96. Muscles of Tongue, Hyoid, and Pharynx 229 97. Stomach 235 98. Colon and Cæcum 238 99. Ileocolic Valve 238 100. Liver 240 101. Liver 240 102. Pancreas and Spleen 242 103. Cartilages of Nose 244 104. Cartilages of Larynx 247 105. Muscles of Larynx 250 106. Bronchi 253 107. Thymus Gland 254 108. Kidney 255 109. Section of Kidney 255 110. Testis 260 111. Male Genital Organs 262 112. Female Urogenital Organs 265 113. Muscles of Urogenital Organs and Anus in Male 270 114. Muscles of Urogenital Organs of Female 272 115. Heart 276 116. Heart 276 117. Inside of Heart 278 118. Vessels of Thorax 282 119. Common Carotid and Internal Jugular 284 120. Branches of External Carotid 288 121. Arteries of Brain 291 122. Vessels and Nerves of the Axilla 295 123. Vessels and Nerves of the Arm 299 124. Palmar Arch 301 125. Cœliac Artery 302 126. Abdominal Blood-vessels 305 127. Medial Vessels and Nerves of the Leg 310 128. Deep Arteries of Foot 314 129. Thoracic Blood-vessels 317 130. Superficial Vessels and Nerves of the Forearm 319 131. Blood-vessels of the Face 322 132. Portal Vein 327 133. Spinal Cord, cranial portion 336 134. Section of Spinal Cord 337 135. Origin of Spinal Nerves 337 136. Cauda Equina, etc. 338 137. Brain, Dorsal View 340 138. Brain, Ventral View 342 139. Diagram of Brain 343 140. Diagram of Brain 343 141. Dorsal View of Midbrain and ’Tween-brain 350 142. Ventral View of Midbrain and ’Tween-brain 352 143. Longitudinal Section of Brain 356 144. Lateral View of Brain 358 145. Diagram of Sulci and Gyri 359 146. Diagram of Sulci and Gyri 361 147. Corpus Callosum 363 148. Fornix, Hippocampus, and Corpus Striatum 364 149. Transverse Section of Brain 366 150. Transverse Section of Brain 366 151. Transverse Section of Brain 366 152. Transverse Section of Brain 367 153. Transverse Section of Brain 367 154. Cranial Nerves 374 155. Nerves of Face 376 156. Cranial Nerves in the Neck 379 157. Sympathetic and Vagus in the Thorax 381 158. Nerves of the Neck 384 159. Brachial Plexus 387 160. Nerves and Vessels of Axilla 389 161. Nerves and Vessels of Forearm 391 162. Lumbar and Sacral Nerves 398 163. Great Sciatic Nerve 401 164. Sympathetic and Vagus in Abdomen 407 165. Nictitating Membrane 410 166. Muscles of Eyeball 411 167. Diagram of Eye 413 168. Cartilage of External Ear 417 169. Muscles of External Ear 419 170. Tympanic Membrane 422 171. Malleus and Incus 423 172. Stapes 424 173. Membranous Labyrinth 425

ANATOMY OF THE CAT.

THE SKELETON OF THE CAT.

The skeleton of the cat consists of 230 to 247 bones exclusive of the sesamoid bones (44) and the chevron bones (8). These are divided as follows: head 35-40, vertebral column 52-53, ribs 26, sternum 1-8, pelvis 2-8, upper extremities 62, lower extremities 54-56. The number of bones varies with the age of the individual, being fewer in the old than in the young animal, owing to the fact that in an old animal some bones that were originally separate have united.

I. THE VERTEBRAL COLUMN. COLUMNA VERTEBRALIS.

The vertebral column, spinal column, or back-bone, consists of a varying number of separate bones, the vertebræ. At its cranial end are seven vertebræ (=cervical=, Fig. 1, _c_) which are without ribs and support the head; caudad of these are thirteen rib-bearing vertebræ (=thoracic=, Fig. 1, _m_); caudad of these are seven that are again without ribs (=lumbar=, Fig. 1, _o_); these are followed by three vertebræ (=sacral=, Fig. 1, _x_) which are united into a single bone, the =sacrum=, which supports the pelvic arch. Following the sacral vertebræ are twenty-two or twenty-three small ribless vertebræ which support the tail (=caudal=, Fig. 1, _y_).

[Illustration: FIG. 1.--SKELETON OF CAT.

_a_, skull; _b_, hyoid; _c_, cervical vertebræ; _d_, clavicle; _e_, scapula; _f_, sternum; _g_, humerus; _h_, radius; _i_, ulna; _j_, carpus; _k_, metacarpus; _l_, phalanges; _m_, thoracic vertebræ; _n_, ribs; _o_, lumbar vertebræ; _p_, innominate bones; _q_, femur; _r_, patella; _s_, fibula; _t_, tibia; _u_, tarsus; _v_, metatarsus; _w_, phalanges; _x_, sacrum; _y_, caudal vertebræ.]

=Thoracic Vertebræ.= =Vertebræ thoracales= (Fig. 4).--The =thoracic vertebræ= are most typical, and the fourth one of these may therefore be first described (Figs. 2 and 3). It forms an oval ring which has numerous processes and surrounds an opening which is the vertebral foramen (_a_). The ventral one-third of this ring is much thickened and forms the =centrum= or body (=corpus=) (_b_) of the vertebra. The centrum is a semicylinder, the plane face of which bounds the vertebral canal, while the curved surface is concave longitudinally and is directed ventrad. The dorsal plane surface of the centrum is marked by a median longitudinal ridge on either side of which is an opening (nutrient foramen) for a blood-vessel. The ends are nearly plane, the caudal being slightly concave; they are harder and smoother than the other surfaces. They may be easily separated in a young specimen as thin plates of bone known as =epiphyses=.

[Illustration: FIG. 2.--FOURTH THORACIC VERTEBRA, CRANIAL END.

FIG. 3.--FOURTH THORACIC VERTEBRA, SIDE VIEW.

_a_, vertebral foramen; _b_, centrum; _c_, caudal, and _d_, cranial, costal demifacets; _e_, radix or pedicle; _f_, lamina; _g_, transverse process; _h_, cranial articular facet; _i_, caudal articular facet; _j_, caudal articular process; _k_, spinous process.]

At the caudal end of the centrum, at its dorsolateral angle, is a smooth area on each side continuous with the surface of the epiphysis and bounded dorsolaterally by a sharp ridge of bone (_c_). It is a =costal demifacet=. In corresponding positions at the cranial end of the centrum are two demifacets not limited by bony ridges (_d_). When the centra of two contiguous thoracic vertebræ are placed together in the natural position the cranial costal demifacets of one together with the caudal demifacets of the other form two =costal= facets (Fig. 4, _e_), one on each side, and each receives the head of a rib.

The dorsal two-thirds of the vertebral ring forms the =vertebral arch= which is continued dorsally into the long, bluntly pointed =spinous process= (Figs. 2 and 3, _k_) for attachment of muscles.

The vertebral arch (each half of which is sometimes called a =neurapophysis=) rises on each side from the cranial two-thirds of the dorsolateral angle of the centrum, as a thickened portion, the radix or pedicle (Figs. 2 and 3, _e_), which forms the ventral half of the lateral boundary of the vertebral canal. From the dorsal end of each radix a flat plate of bone, the =lamina= (_f_), extends caudomediad to join its fellow of the opposite side and form the vertebral arch. Owing to the fact that the radix rises from only the cranial two-thirds of the centrum there is left in the caudal border of the vertebral arch a notch bounded by the radix, the lamina, and the centrum. There is also a slight excavation of the cranial border of the radix. When the vertebræ are articulated in the natural position, these notches form the =intervertebral foramina= (Fig. 4, _d_), for the exit of the spinal nerves.

At the junction of radix and lamina the arch is produced craniolaterad into a short process, the =transverse process= (_g_), knobbed at the end. On the ventral face of its free end the transverse process bears a smooth facet, the transverse costal facet or tubercular facet (Fig. 4, _c_), for articulation with the tubercle of a rib.

On the dorsal face of each lamina at its cranial border is a smooth oval area, the =cranial articular facet= (superior articular facet of human anatomy) (Figs. 2 and 3, _h_). Its long axis is oblique and it looks dorsolaterad. The slight projections of the cranial edge of the laminæ on which the facets are situated are the inconspicuous =cranial articular processes= (prezygapophyses).

On the ventral surface of each lamina at the caudal border, near the middle line is a similar area, the =caudal articular= =facet= (inferior articular facet of human anatomy) (_i_); these occupy the ventral surfaces of two projections which form the =caudal= (inferior) =articular processes= (postzygapophyses) (_j_). These are separated by a median notch. When the vertebræ are in their natural position the caudal articular facets lie dorsad of the cranial facets and fit against them. They thus strengthen the joint between contiguous vertebræ, while permitting slight rotary motion.

[Illustration: FIG. 4.--THORACIC VERTEBRÆ, SIDE VIEW.

_a_, spinous processes; _b_, cranial articular processes; _c_, transverse costal facets; _d_, intervertebral foramina; _e_, costal facets; _f_, accessory processes; _g_, mammillary processes; _h_, caudal articular processes.]

=Differential Characters of the Thoracic Vertebræ= (Fig. 4).--Following the thoracic vertebræ caudad there is to be seen a gradual increase in the size of the centra brought about by an increase in their craniocaudal and transverse measurements. The dorsoventral measurements remain nearly the same. The costal facets (Fig. 4, _e_) shift caudad so that on the eleventh, twelfth, and thirteenth thoracic vertebræ each lies entirely on the cranial end of its centrum, while the caudal end of the centrum immediately preceding is not marked by any part of it. In the eleventh thoracic vertebra each costal facet is usually still confluent with the smooth cranial end of the centrum. In the twelfth vertebra the facets are separated by smooth ridges from the cranial end of the vertebra, while in the thirteenth vertebra they are separated by rough ridges.

The spinous processes (_a_) of the first four are of about the same length. They then decrease in length to the twelfth, while the twelfth and thirteenth are slightly longer than the eleventh. The first ten slope more or less caudad, while the spinous process of the tenth (=anticlinal=) vertebra is vertical and those of the eleventh, twelfth, and thirteenth point craniad.

Each of the transverse processes of the seventh thoracic vertebra shows a tendency to divide into three tubercles; one of these is directed craniad, the mammillary process (or metapophysis), one caudad, the accessory process (or anapophysis), while the third (transverse process proper) looks ventrad and bears the transverse costal facet. This division becomes more prominent in the succeeding vertebræ, being most marked in the ninth and tenth. In the eleventh, twelfth, and thirteenth vertebræ the mammillary (_g_) and accessory (_f_) processes are very pronounced, while the transverse costal facet and that part of the transverse process which bears it have disappeared. The ribs of the eleventh, twelfth, and thirteenth vertebræ are thus attached to their respective centra by their heads alone.

The cranial articular processes (_b_) are prominent on the first two thoracic vertebræ; back of these they are very small as far as the eleventh, so that the articular facets seem to be borne merely upon the dorsal surface of the cranial edge of the laminæ. In the eleventh, twelfth, and thirteenth the cranial articular processes are large, bearing the articular facets on their medial surfaces, while the mammillary processes appear as tubercles on the lateral surfaces of the articular processes. The caudal articular processes (_h_) are prominent in the first thoracic, then smaller until the tenth is reached; in the tenth, eleventh, twelfth, and thirteenth they are large and their facets are borne laterally, so as to face the corresponding cranial facets. Thus from the tenth to the thirteenth thoracic vertebra rotary motion is very limited, owing to the interlocking of the articular processes.

=The Lumbar Vertebræ.= =Vertebræ lumbales= (Fig. 5).--The last thoracic vertebræ form the transition to the typical lumbar vertebræ. These are larger than the thoracic vertebræ. The centra are of the form of the centra of the thoracic vertebræ, and increase in length to the sixth, but the seventh is about the length of the first. They increase in breadth to the last.

[Illustration: FIG. 5.--LUMBAR VERTEBRÆ.

_a_, cranial articular processes; _b_, mammillary processes; _c_, caudal articular processes; _d_, accessory processes; _e_, transverse processes; _f_, spinous processes.]

The cranial articular processes (Fig. 5, _a_) are prominent and directed craniodorsad; they have the facets on their medial surfaces, while their dorsolateral surfaces bear the mammillary processes (_b_) as prominent tubercles. The caudal articular processes (_c_) are likewise large; their facets look laterad. When the vertebræ are articulated they are received between the medially directed cranial processes.

The accessory processes (_d_) are well developed on the first vertebra, diminish in size to the fifth or sixth, and are absent on the seventh and sometimes on the sixth.

The transverse processes (more properly pseudo-transverse processes) (_e_) arise from the lateral surface of the centra; are flat and are directed ventrocraniolaterad. The first is small, and they increase in length and breadth from the first to the sixth, those of the last being slightly smaller than in the sixth. The free ends of the last four are curved craniad.

The spinous processes (_f_) are flat and directed craniodorsad. They increase in length to the fifth and then decrease. The first five are knobbed at the end. In a dorsal view the spinous process and cranial articular processes of each vertebra are seen to interlock with the caudal articular processes and accessory processes of the preceding vertebra in such a way as to prevent rotary motion, and this arrangement may be traced craniad as far as the eleventh thoracic vertebra.

=Sacral Vertebræ.= =Vertebræ sacrales= (Figs. 6 and 7).--The three sacral vertebræ are united in the adult into a single bone, the =os sacrum=, or =sacrum=. In a kitten the three vertebræ are separate, while in an animal almost mature the first two are united and the third is still separate. The sacrum lies between the last lumbar and the first caudal vertebræ and articulates laterally with the two innominate bones. It is pyramidal, with the base of the pyramid directed craniad, and is perforated by a depressed longitudinal canal, the =sacral canal=, which is a continuation of the vertebral canal, and by four large foramina dorsally and four ventrally. It may be described as having a cranial end or base and a caudal end or apex, a dorsal, a ventral, and two lateral surfaces.

The =base= is slightly oblique and presents a smooth transversely oval articular facet (the cranial end of the centrum of the first sacral vertebra), for articulation with the centrum of the last lumbar vertebra. Dorsad of this is the sacral canal, more depressed than the vertebral arch craniad of it. It supports a spinous process (Fig. 6, _a_) which is directed dorsad. At the junction of its lamina and radix is seen the prominent cranial articular process (_b_) with sometimes slight indications of a mammillary process on its lateral surface. Laterad of the articular facet is seen the cranial face of the expanded “pseudo-transverse process” (_c_) of the first sacral vertebra. The ventral border of the base is concave ventrad, forming an arc of about 120 degrees. The =apex= shows the caudal end of the last sacral centrum. Dorsad of this are the vertebral arch with a very short spinous process (_a′_), and the caudal articular processes (_d_). Laterad of the centrum appears the laterally directed thin transverse process (_e_).

[Illustration: FIG. 6.--SACRUM, DORSAL SURFACE.

FIG. 7.--SACRUM, VENTRAL SURFACE.

Fig. 6.--1, 2, 3, the three sacral vertebræ. _a_, _a′_, spinous processes; _b_, cranial articular process of first sacral vertebra; _c_, expanded transverse process of first sacral vertebra; _d_, caudal articular processes of third sacral vertebra; _e_, transverse processes of third sacral vertebra; _f_, tubercles formed by fused articular processes of the vertebræ; _g_, dorsal (or posterior) sacral foramina.

Fig. 7.--1, 2, 3, the three sacral vertebræ. _a_, the transverse ridges formed by the union of the centra; _b_, cranial articular processes of first vertebra; _c_, transverse process of first vertebra; _d_, caudal articular processes of third vertebra; _e_, transverse processes of third sacral vertebra; _f_, _f′_, ventral (or anterior) sacral foramina; _g_, notch which helps to form third ventral sacral foramen.]

The ventral or pelvic surface (Fig. 7) is smooth, concave craniad, convex caudad, and crossed by two transverse ridges (_a_) along which are seen the ossified remains of the intervertebral fibro-cartilages. At the ends of the first ridge is a pair of nearly circular =ventral= (or anterior) =sacral foramina= (_f_) for the passage of sacral nerves. At the end of the second ridge is a pair of ventral sacral foramina (_f′_), smaller than the first pair and continued laterocaudad into shallow grooves for the ventral rami of the sacral nerves. That portion of the bone lying laterad of a line joining the medial borders of these two pairs of foramina is known as the =lateral mass= of the sacrum and is composed of the fused transverse processes of the sacral vertebræ. At the caudal margin of the ventral surface there is a notch between the lateral mass and the centrum (_g_). When the caudal vertebræ are articulated, this notch helps to form a foramen for the third sacral nerve.

The dorsal surface (Fig. 6) is narrower at its cranial end than is the ventral surface. Its cranial border bears laterally a pair of cranial articular processes (_b_) with their medially directed facets and between them it is concave, so that a large dorsal opening is left into the vertebral canal between the last lumbar vertebra and the sacrum. Caudad of the articular processes are two pairs of tubercles (_f_). These are the fused cranial and caudal articular processes of the sacral vertebræ. Caudad of them are the caudal articular processes of the last sacral vertebra (_d_). Craniolaterad of the middle and cranial tubercles are =dorsal= (posterior) =sacral foramina= (_g_) for the transmission of the dorsal rami of the sacral nerves. Three spinous processes (_a_) appear between these rows of tubercles. They decrease in height caudad. That part of the surface included between the spinous process and the tubercles is made up of the fused laminæ of the sacral vertebræ. That part between the tubercles and a line joining the lateral margins of the dorsal (posterior) sacral foramina is formed by the fused radices of the sacral vertebræ.

The lateral surface may be divided into two parts. Craniad is a large rough triangular area with equal sides and with one of its angles directed ventrocraniad. It is the lateral face of the pseudo-transverse process of the first sacral vertebra (Fig. 6, _c_). A smooth curved surface (the auricular facet) along its ventral edge articulates with the ilium, while the dorsal portion is rough for attachment of ligaments. Caudad is the narrow longitudinal triangular area of the lateral faces of the fused transverse processes of the second and third sacral vertebræ.

=Caudal Vertebræ.= =Vertebræ caudales= (Fig. 1, _y_, and Figs. 8 and 9).--The caudal vertebræ (21-23 in number) decrease gradually in size to the last one. Caudad they become longer and more slender and lose the character of vertebræ. They become finally reduced to mere centra,--slender rods of bone knobbed or enlarged at their two ends (Fig. 8). The last one is more pointed than the others and bears at its caudal end a small separate conical piece, the rudiment of an additional vertebra.

[Illustration: FIG. 8.

FIG. 9.

Fig. 8.--Caudal Vertebra, from near the caudal end of the tail.

Fig. 9.--Fourth Caudal Vertebra, ventral view. _a_, transverse processes; _b_, cranial articular processes; _c_, hæmal processes; _d_, chevron bone.]

The parts of a typical vertebra--vertebral arch, transverse processes, cranial and caudal articular processes--may be recognized in the vertebræ as far back as the eighth or ninth. The transverse processes (Fig. 9, _a_) are directed caudad and decrease rapidly in length. They are very small on the ninth vertebra, but may be recognized for a considerable distance back of this. The spinous process disappears at about the fourth caudal vertebra, and the vertebral canal becomes gradually smaller caudad, until on the eighth or ninth vertebra it becomes merely a groove open dorsad.

Caudad of the third vertebra for a considerable distance, each centrum bears on each lateral face at its cranial end a short =anterior transverse= process, and on its ventral face at its cranial end a pair of rounded tubercles, =hæmal processes= (_c_), which articulate with a small pyramidal =chevron= bone (_d_) so as to enclose a canal. These structures disappear caudad.

=Cervical Vertebræ.= =Vertebræ cervicales= (Fig. 10).--The cervical vertebræ number seven. The first two of these are so peculiar as to require a separate description, so that the last five may be first considered.