104 COMPARATIVE OSTEOLOGY. 



the single oue of the horse, the external one being always the smaller ; a rudi- 

 mentary metacarpal is placed postero-externally. The phalanges and sesamoids 

 in either limb are double, one complete set forming each digit ; they are small 

 and narrow, the coffin bone resembling half of that of the horse, mesially 

 divided. Posterior to the fetlock joint are two rudimentary digits, each con- 

 taining two undeveloped phalanges, the median and the distal. 



PELVIS. 



The os innominatum is larger, but presents the same general appearance as 

 in the horse. The ilium is thick, and possesses a prominent line running from 

 the anterior spine to the superior ischiatic ridge. The internal surface is very 

 convex, the ridge between the part resting on and that without the sacrum 

 being well marked. The ilio-pectineal eminence is prominent, and the crest 

 and spines very strong. The ischium equals the ilium in size ; the anterior 

 extremity has a thick projecting external portion, which forms part of the 

 cotyloid cavity, and is surmounted by the large superior ischiatic spine, whence 

 a slight ridge is continued backwards over the thick concave body to the tuber- 

 osity. The inferior ischiatic spine is conical, pointing outwards and down- 

 wards. The ischial symphysis presents inferiorly a ridge and tubercle, absent 

 in the horse. The pubis is large and concave, and the symphysis is never 

 completely ossified. The acetabulum is deep, and the cotyloid notch is narrow 

 and deep, being near the large foramen ovale. The inlet of the pelvic 

 cavity is oval ; its sacro-pubic diameter is greater than the transverse one, 

 while the sacro- ischiatic diameter of the outlet is less than the transverse. 



PELVIC LIMB. 



The femur (Fig. 25. I) is distinguished from that of the horse by the 

 trochanter minor being wanting. The trochanter internus is a round tubercle 

 near the posterior surface ; the head is small, but prominent, the trochanteric 

 fossa deep, but small ; the trochanter major has only one eminence, not very 

 prominent, and is united to the internal trochanter by a ridge. The condyles 

 and trochlea are somewhat small, and the supracondyloid fossa is shallow. 

 The patella, is narrow, and somewhat conical in shape. 



The tibia (Fig. 25. n'} has no vertical fossa on the anterior tuberosity, and no 

 articular facet for the fibula ; the distal extremity has its external malleolus 

 detached, forming a small bone called the malleolar bone, which articulates 

 with the tibia, calcaneum, and astragalus, and represents the distal end of the 

 fibula, the remainder of which bone, small when present, is usually replaced 

 by a long ligament stretching the whole length of the tibia. 



The tarsus consists of 5 bones. The astragalus is deep, but narrow, having 

 a pulley-shaped surface inferiorly as well as superiorly. The calcaneum is 

 long and square ; the cuneiforme magnum and cuboid are united, forming the 

 cubo-cuneiform bone ; the cuneiforme medium is like that of the horse, while 

 the parvum is very small. 



The large metatarsal bone has its inferior extremity divided into two equal 

 parts by a deep fissure, with a groove superiorly. The small metatarsal bones, 

 when present, are rudimentary and single. The digits correspond to those of 

 the pectoral limb. 



