200 SHUFELDT. 



the weight of the body in standing and walking, transmitted to it from 

 the tibia, and to a very slight degree the libula. Quadrupeds have this 

 weight variously divided, while in Gynocephaliis it appears that this tibio- 

 tarsal joint sees its chief use as an enarthrodial articulation. Usually the 

 very irregularly-shaped astragalus is described as having a head, a neck, 

 and a body, and such divisions are easily made out. '^Mien duly arti- 

 culated, the head projects to the front in line with the scaphoid, the 

 cuneifomi bones, and the first and second toes. Anteriorly the head has a 

 large, smooth, convex facet which articulates with a concavity in the 

 scaphoid and a surface on the antero-superior aspect of the os ealcis.-'' 

 The latter encroaches upon the surface of the neck beneath. The neck 

 is somewhat compressed from above downward (here really from side to 

 side), and is wider in the opposite direction. The entire upper part of 

 the body is occupied by an elegant, smooth, convex facet for articulation 

 with the two bones of the leg. This articular surface is carried over upon 

 the sides of the astragakis, and here the malleoli of the aforesaid bones 

 articulate, as is the ease with nearlj' all mammals. Fibula gets the smaller 

 share, a little less than one-half of this articulation. Posteriorly and 

 beneath we note a well-marked groove, which in life gives passage to the 

 tendon of the flexor longus hallucis muscle. On the sides there are pits 

 for the attachment of ligaments. At the center of the bone^ on the side 

 next to the os calcis in articulation, there is an irregular concavity; this 

 is on the neck, while posterior to it on the body there is an elliptical 

 facet for a similar one on the caleaneum. No muscle either arises from, 

 or is inserted upon, the astragalus, and as pointed out above the astragalus 

 articulates with four bones : tibia, fibula, caleaneum, and scaphoid. 



The os calcis or caleaneum, is longer, narrower, and larger than the 

 astragalus; the latter projects just a trifle more to the front, while the 

 former exceeds it in length behind. Altogether the bone is very irregular 

 in form and has the tendons of a number of muscles and ligaments 

 attached to it, or arising from it. Os calcis is the tarsal that forms the 

 skeletal part of the heel and here we find this posterior extension to be 

 a distinct semi-ellipsoidal projection, subvertieally placed upon the body of 

 the bone. This is generally called its tuberosity, and upon it is inserted 

 the tendo Achillis. Beyond it, the body of the bone is somewhat con- 

 stricted and compressed from side to side. Mesially, it throws out a 

 conspicuous triangular process, the upper side of which articulates with 

 the under side of the neck of the astragalus. A similar, rather smaller, 



" In assigning directions, and the directions in whieli surfaces look or face, 

 for the salie of convenience, it is assumed tliat the animal stands on the gi-ound 

 as do ordinary quadrupeds, otherwise it would be very difficult to appreciate 

 the relations of the tarsus to the rest of the skeleton, and the most unusual posi- 

 tion in which the foot is held with respect to the surface upon which the animal 

 is traveling. 



