526 



Genus Equus. 



3133. The skeleton of a Horse (Equus Caballus). 



The vertebral formula is : 7 cervical, 19 dorsal, 5 lumbar, 5 sacral, and 17 caudal. Eight 

 pairs of ribs directly join the sternum, which consists of seven bones and an ensiform cartilage. 

 The neural arches of the last five cervical vertebrae expand above into flattened, subquadrate, 

 horizontal plates of bone, with a rough tubercle in place of a spine : the zygapophyses are 

 unusually large. The perforated transverse process sends a pleurapophysis downwards and 

 forwards, and a diapophysis backwards and outwards, in the third to the sixth cervical inclu- 

 sive : in the seventh the diapophysial part alone is developed, and is imperforate. The 

 spinous processes suddenly and considerably increase in length in the first three dorsals, and 

 attain their greatest length in the fifth and sixth, after which they gradually shorten to the 

 thirteenth, and continue of the same length to the last lumbar. The metapophysis, com- 

 mencing as a tuberosity above the diapophysis, passes gradually from that part to the outer 

 side of the prozygapophysis, which it finally attains in the seventeenth dorsal vertebra, and 

 continues in the same place throughout the lumbar series. There are no anapophyses. The 

 lumbar diapophyses are long, broad, and in close juxtaposition ; the last presents an articular 

 concavity adapted to a corresponding convexity on the fore part of the diapophysis of the first 

 sacral. The spine of the scapula has no acromion. The ulna, represented by its olecranal 

 extremity, is confluent with the radius. The os magnum in the second series of carpal bones 

 is remarkable for its great breadth, corresponding to the enormous development of the meta- 

 carpal bone of the middle toe, which forms the chief part of the foot. Splint-shaped rudi- 

 ments of the metacarpals, answering to the second and fourth of the pentadactyle foot, are 

 articulated respectively to the trapezoides and the reduced homologue of the unciforme. The 

 femur is characterized by a third trochanter developed from the outer part of the shaft before 

 the great trochanter. There is a splint-shaped rudiment of the proximal end of the fibula, 

 but not any rudiment of the distal end. The external cuneiforme is the largest of the second 

 series of tarsals, being in proportion to the metatarsal of the large middle digit, which it 

 mainly supports. The diminished cuboides articulates partly with this, partly with the rudi- 

 ment of the metatarsal corresponding with that of the fourth toe. A similar rudiment of the 

 metatarsal of the toe corresponding with that of the second articulates with a cuneiforme 

 medium here, however, the innermost of the second series of tarsal bones. 



Hunterian. 



3134. The skeleton of the dwarf variety of Equus Caballus, commonly called the 

 ' Shetland pony.' Mus. South. 



3135. The skull, with the stylohyals artificially attached, of an aged Horse (Equus 

 Caballus). 



Here the maxillo-premaxillary sutures, and most of the other sutures of the cranium, have 

 been obliterated. The crowns of the incisors are worn down almost to the obliteration of the 

 ' mark,' which is due to a central inflected fold of enamel and cement. 



Hunterian. 



