.M E (} A L O i\ Y X . 25 



vening surfaces form trilateral concavities, roughened in many places with reticu- 

 lar risings, more especially near the base of the bone, for muscular attachment. 



The dorsum (PI. VIII, Fig. 1), as in Mi/loduii, is nearly equally divided by the 

 spine into two deeply concave fossae, which ara I'oughened with reticular ridges. 



The infrarspiuatus fossa is strengthened below by a prominent ridge, commencing 

 in a gradual manner at the base, about two inches from the posterior angle, and 

 proceeding forward to form the anterior portion of the inferior costa of the scapula. 

 At the cervix the fossa is impressed with a pair of broad, shallow, vascular channels, 

 diverging into a number of branches at the root of the spine. In the course of two 

 of the latter branches are large nutritious foramina. 



The suprarspinatus fossa at its lower part is more capacious than the correspond- 

 ing portion of the infra-spinatus fossa, and at the side of the root of the coracoid 

 process it is pierced by a nearly circular coracoid foramen, a little over an inch in 

 diameter. From the latter, two feebly marked vascular channels proceed to the 

 root of the spine, at which position one of them is continuous with a large nutri- 

 tious foramen. 



The base of the scapula is antero-posteriorly convex, and forms a thickened 

 boundary to that part of the bone. 



The specimen of the posterior angle of the left scapula, in Dr. Dickeson's col- 

 lection, presents an irregular cicatrix, in the course of which is a crooked foramen 

 over an inch in length, indicating the former existence of a fracture of this por- 

 tion of the bone during the life of tlie animal. This is another instance added to 

 those previously given, proving the great liability of the giant sloths to accidents 

 resulting in fracture of the bones. 



The spine commences in a broad, trilateral, roughened surface at the base of the 

 bone, and gradually rises until it arches over the outlet of the supra-spinatus fossa 

 to become confluent with the coracoid process. Its root appears very thick from the 

 fact that the dorsum of the bone is elevated in a pyramidal manner to support it. 



The coraco-acromial arch (PI. VIII, Fig. 2) is five inches long, and at its broadest 

 part is about two inches wide; and it is elevated over two inches from the bottom 

 of the supra-spinatus fossa. 



The glenoid articulation (Fig. 2) is three and three-quarter inches long, and a 

 little less than two and a half wide; and it presents the same form as that in Dr. 

 Owen's specimen already described. 



The estimated length of the scapula, from the summit of the coracoid process to 

 the posterior angle, is one foot and a half. 



The specimen of a young scapula, in the collection of the Academy of Natural 

 Sciences, is interesting in relation to the mode of development of several of i(s 

 parts. It is of the left side, and with the exception of the coi'aco-acroraial arch, 

 and superior margin, and a large hole through the infra-spinatus fossa, is nearly 

 perfect. (PI. VIII, Fig. 3, 4.) The coracoid process exists as a distinct bone, which 

 is compressed cylindroid at its middle, and dilated towards the extremities. (Fig. 3, 

 A.) The base of the coracoid bone is received into a deep angular notch (Fig. 3, 

 A, b), between the coracoid foramen and an epiphysis (Fig. 3, c), which forms the 

 anterior half of the glenoid articulation ; and the other extremity presents a rough 



