Mackintosh — Mmcular Aiujtomy of Choloepus, didactylus. 67 



habits of the two creatures led us to expect a close correspondence in 

 the arrangement of their muscles. The weights of most of the muscles 

 are given in decimals of an ounce, in a tabular form at the end of the 

 Paper (vide p. 78). 



In the head, we noticed the Eustachian tube opening as an oblique 

 pit just in frunt of the external pterygoid, and placed in front of it was 

 a distinct depression leading upwards, the termination of which we en- 

 deavoured to find, but in vain, and hence wei^e unable to surmise its 

 function. The mucous membrane of the cheek was studded with 

 rows of papiilse ; the parotid and submaxillary glands were united, but 

 no trace of a sublingual existed. Other points of interest in general 

 anatomy were — the well-developed condition of the stylomaxillary fold 

 of fascia, which extended along the whole length of the hyoid arch; 

 the very strong spinoglenoid ligament; the well-developed condition of 

 the ligaments of Flood and Humphry; a remarkable fibrous band 

 passing from the front aspect of the humeral trochanter to the anterior 

 ulnar attachment of the orbicular ligament ; the very deep supra- 

 olecranal pit in the humerus ; the limited degree of rotation of the 

 radius (one-fifth of a circle) ; the absence of the round ligament of the 

 hip joint, as is usual in sloths ; the strong mucous ligament of the knee 

 joint ; and the curious arrangement of the ligaments in the ankle joint. 

 Of these the external lateral extended from the fibula in three slips, an 

 anterior attached to the outer tubercle of the astragalus, a middle at- 

 tached to the bod}^ of that bone, and a posterior to the calcaneum, a 

 deep slip of which dips into the base of the astragalus; a large number 

 of fibres extend between these two bones and form an astragalo- 

 calcaneal ligament; the internal lateral is strong and thick, running 

 from the inside of the internal malleolus to the astragalus ; the anterior 

 ligament is weak. 

 The principal muscles of th6 head were : — 



Massetericus clothes the descending process of the jugal, and be- 

 comes fused near its insertion with temporalis, which was normal. 



Buccinator had its fibres running mainly in an anterior direction. 



Zygomaticus arises from the front of the jugal process. 

 In the neck and trunk we found the following arrangements : — 



Splenius, with an occipital insertion, has its origin from the trans- 

 verse processes of all the cervical vertebrae, and from the front of com- 

 plexus, which has a similar cervical origin, but includes the first 

 dorsal also, and is inserted into the occiput. 



Longus colli is remarkable only for its strength. 



Obliquus colli superior arises from the transverse processes of the 

 four upper cervical vertebrae, and is inserted into the front of the atlas, 

 wliilst its inferior part extends from the first three dorsals to the trans- 

 verse process of the seventh cervical. 



Rectus colli stretches from the second and third dorsals to the 

 atlas. 



Rectus capitis anticus major was curiously arranged, taking origin 



