Part 37

The vertebral formula is C{7}T{13}L{7(6)}S{3}Cy_{20–23}.

The =cervical vertebræ= are relatively longer than in the ox and the pig. The bodies of the typical vertebræ diminish in length from first to last and are compressed dorso-ventrally. The anterior extremity is moderately convex and the posterior slightly concave; both are oblique. The median ridge and lateral grooves on the upper surface of the body are very well marked. The second, third, and fourth have distinct ventral spines. The spinous process of the third has the form of a long low crest; in the remainder it is higher, blunt-pointed, and inclined forward. The transverse processes of the third, fourth, and fifth project downward and backward, and divide into two branches; of these, the anterior one is thin, and the posterior is thick and tuberculate at its free end. The process of the sixth has two parts; one of these is an extensive quadrilateral plate directed downward and outward and ridged on its inner surface; the other part is short and blunt, and is directed outward and a little backward and upward. The seventh is readily distinguished by its shortness, the length of its spine, and the single transverse process. The posterior articular processes bear tubercles which are large on the third, fourth, and fifth.

The ventral arch of the =atlas= is narrow from before backward, and bears a small tubercle posteriorly. The upper surface of the dorsal arch is strongly convex and rough centrally. The wings are wide, flattened, and almost horizontal. The upper surface is rough. There is an alar notch (Incisura alaris) on the anterior border instead of the anterior foramen. The foramen transversarium is present.

The body of the =axis= is flattened dorso-ventrally, especially in front. The odontoid process is rounded and relatively long, reaching almost to the occipital bone; it is inclined upward a little. The articular surfaces which flank it are condyloid in form and very oblique. The inferior surface is wide, and is divided by a median crest into two fossæ. The transverse processes are single, pointed, directed backward and outward, and perforated by relatively large foramina transversaria. The spinous process is thin and of moderate height, but very long; it is prolonged forward so as to overhang the dorsal arch of the atlas, and is terminated behind by a tuberosity which is connected by two crests with the posterior articular processes. The anterior notches are large and are never converted into foramina.

The bodies of the =thoracic vertebræ= are wide and compressed dorso-ventrally, especially at each end of the region. Their convex anterior surfaces are depressed in the middle. The posterior facets for the heads of the ribs are absent on the last three or four. The transverse processes resemble those of the horse. They bear mammillary processes except at the anterior end of the region. The facets for the tubercles of the ribs are large and concave in the anterior part of the series, and become smaller and slightly convex further back. The last three have accessory processes also. The first three or four spinous processes are about equal in length. Behind this they become gradually shorter to the tenth, and then remain equal. The backward slope is most marked in the ninth and tenth. The eleventh is practically vertical (anticlinal vertebra) and the last two incline slightly forward.

The bodies of the =lumbar vertebræ= are decidedly flattened dorso-ventrally, and increase in width from first to last. The length increases to the sixth. The transverse processes are plate-like and are directed forward and downward. Their length increases to the fifth and sixth. They form no joints with each other or with the sacrum. Their extremities are enlarged, with the exception of the last. The accessory processes project backward over the posterior notches of the first five. The anterior articular processes are large, compressed laterally, and bear mammillary processes. The spinous processes are broad below, narrower above, and with the exception of the last, incline a little forward. Their height diminishes behind the fourth.

FIG. 115.—SKELETON OF DOG, LATERAL VIEW.

a, Cranium; b, face; c, mandible; 1H-7H, cervical vertebræ; 13B, last thoracic vertebra; 1L-7L, lumbar vertebræ; K, sacrum; S, coccygeal vertebræ; 1R-13R, ribs; R.Kn., costal cartilages; St., sternum; d, scapula; d′, supraspinous fossa; d″, infraspinous fossa; 1, spine of scapula; 2, acromion; 3, tuberosity of scapula; 3′, articular end of scapula; e, humerus; 4, head of humerus; 5, external tuberosity of humerus; 5′, deltoid ridge; 6, 6′, epicondyles of humerus; 7, external condyloid crest; 7′, coronoid fossa; f, radius; g, ulna; 8, olecranon; 9, “beak” of ulna; h, carpus; i, metacarpus; k, proximal phalanges; l, middle phalanges; m, distal phalanges; n, sesamoid; p, ilium; 10, wing of ilium; 11, shaft of ilium; 12, crest of ilium; 13, external angle of ilium (tuber coxæ); 14, internal angle of ilium (tuber sacrale); 15, superior ischiatic spine; q, pubis; r, ischium; 16, tuber ischii; 17, acetabulum; s, femur; 18, head of femur; 19, trochanter major; 20, trochanter minor; 21, trochanter tertius; 22, 23, condyles; 24, 25, epicondyles; 26, trochlea; t, patella; u, tibia; 27, tuberosity of tibia; 28, 29, condyles of tibia; 30, internal malleolus; v, fibula; 31, external malleolus; 32, head of fibula; w, tarsus; x, metatarsus; y, phalanges; 33, occipital bone; 34, paramastoid (styloid) process; 35, parietal bone; 36, frontal bone; 37, lacrimal bone; 38, malar bone; 39, squamous temporal; 40, maxilla; 40′, infraorbital foramen; 41, premaxilla; 42, nasal bone; 43, external auditory meatus; 44, canine tooth; 45, masseteric fossa; 46, angular process of mandible. (After Ellenberger, in Leisering’s Atlas.) ]

The =sacrum= results from the early fusion of three vertebræ. It is short, wide, and quadrangular. The spines are fused to form a median crest, which is notched, however, between the summits of the spines. On either side are two tubercles, vestiges of the fused articular processes. The pelvic surface is deeply concave and presents two pairs of foramina. The wings are prismatic and very high. Their lateral surfaces are extensive, face almost directly outward, and bear an auricular surface on the lower part. The anterior surface of the body of the first vertebra is extensive, depressed in its middle, and bears a prominent lip below. The anterior articular processes are large and have extensive, slightly concave facets which face upward and inward. The posterior articular processes are small. The transverse processes of the last vertebra project backward and may articulate or fuse with those of the first coccygeal. The sacral canal is strongly compressed dorso-ventrally.

FIG. 116.—ATLAS OF DOG, VIEWED FROM ABOVE AND BEHIND.

a, Wing; b, dorsal arch and tubercle; c, ventral tubercle; d, intervertebral foramen; e, foramen transversarium; f, articular surface for axis. (Ellenberger-Baum, Anat. d. Hundes.) ]

FIG. 117.—AXIS OF DOG, LEFT LATERAL VIEW.

a, Odontoid process; b, articular surface for atlas; c, transverse process; d; foramen transversarium; d′, posterior opening of d; e, spine; f, posterior articular process. (Ellenberger-Baum, Anat. d. Hundes.) ]

The =coccygeal vertebræ= are fully developed in the anterior part of the region. The arch is complete in the first six usually. The first three or four have well developed articular processes at each end. Behind this the posterior pair quickly disappears, and the anterior ones become non-articular and gradually reduced in size. The transverse processes of the first five or six are relatively large; behind this they quickly disappear. =Hæmal arches= (or chevron bones) in the form of a =V= or =Y= occur ventrally at the intercentral junctions of the third, fourth, and fifth usually. They transmit the middle coccygeal artery, which passes between pairs of ventral tubercles further back.

FIG. 118.—SIXTH CERVICAL VERTEBRA OF DOG, LEFT VIEW.

a, Ventral plate, b, lateral part of transverse process; c, foramen transversarium; d, anterior articular process; f, accessory process; g, spinous process; h, articular head of body. (Ellenberger-Baum, Anat. d. Hundes.) ]

FIG. 119.—FOURTH THORACIC VERTEBRA OF DOG, LEFT VIEW.

a, Head; b, glenoid cavity; c, facet for head of rib; d, transverse process; e, facet for tubercle of rib; f, mammillary process; g, posterior articular process; h, spinous process. (Ellenberger-Baum, Anat. d. Hundes.) ]

=Curves.=—A gentle curve, convex ventrally, is formed by the cervical and the anterior part of the thoracic region. The posterior thoracic and the lumbar vertebra form a second curve, concave ventrally. The sacral promontory is well marked. The sacrum and the anterior part of the coccygeal region constitute a third and more pronounced curve, concave ventrally. In long-tailed dogs the sacro-coccygeal region is somewhat =S=-shaped.

=Variations.=—Numerical variations are not common except in the coccygeal region. The number of thoracic vertebræ may be twelve or fourteen, with or without compensatory change in the lumbar region. Girard recorded a case with eight lumbar and the usual number of thoracic vertebra. Six lumbar with fourteen thoracic vertebræ have been met with. The first coccygeal sometimes unites with the sacrum.

THE RIBS

Thirteen pairs of ribs are present, of which nine are sternal and four asternal. They are strongly curved, narrow, and thick. Those in the middle of the series are the longest. The first eight or nine increase in width in their lower part. The last rib is usually floating. The costal cartilages are long and curve forward; the length and curvature of the first pair is a striking special feature.

FIG. 120.—FOURTH LUMBAR VERTEBRA OF DOG, LEFT VIEW.

a, b, Articular surfaces of body; c, transverse process; d, accessory process; e, anterior articular process; e′, mammillary process; f, posterior articular process; g, spinous process. (Ellenberger-Baum, Anat. d. Hundes.) ]

FIG. 121.—SACRUM OF DOG, DORSAL VIEW.

a, Dorsal sacral foramina; b, articular surface of body of first segment; c, d, anterior articular processes; e, wing; f, rudiments of articular processes; g, lateral part; h, spinous processes. (Ellenberger-Baum, Anat. d. Hundes.) ]

THE STERNUM

This is long, laterally compressed, and consists of eight sternebræ, which fuse only in exceptional cases and in extreme old age. The first segment is the longest; its anterior end is blunt-pointed and bears a short conical cartilage. It widens at the point of articulation of the first pair of cartilages. The last segment is also long, thinner than its predecessors, wide in front, and narrow behind, where it bears a narrow xiphoid cartilage.