130 



rabbit; and Messrs. Mivart and Murie have found it supplying two 

 digits in the hare and crested agouti (" Proceedings of the Zoological 

 Society," 1866, p. 405). The extensor annularis longus above de- 

 scribed is a different muscle from the extensor of this finger, which I 

 referred to in my former paper (" Proceedings of the Eoyal Irish 

 Academy," April, 1866), which was a part of the extensor digitorum 

 brevis manus. 



20. I have not met with any additional cases of double interossei ; 

 but I would wish to remark, in this place, that the theory which I put 

 forward in my former paper has obtained a striking confirmation from 

 comparative anatomy in the structure of the manus of the Hyrax capen- 

 sis. Messrs. Murie and Mivart, in their admirable memoir upon the 

 myology of this species, note that there exist four pair of interossei on 

 the palmar surface of the metacarpal bones, arising from the aponeuro- 

 tic investment of their proximal end, and inserted into sesamoid bones, 

 one on each side of the distal end of the metacarpals ; the sesamoid 

 bones acting upon the proximal phalanges by means of connecting- 

 fibres. There are also four larger aberrant muscles developed in this 

 animal, which most probably are displaced dorsal interossei (" Pro- 

 ceedings of the Zoological Society," 1865, part ii. p. 343). Mr. Wood 

 has suggested to me that, in his cases of double interossei, the first 

 palmar interosseous had a bifurcate origin from the second and third 

 metacarpal bones, and the interosseous of the thumb had likewise an 

 attachment to the first and second. This was likewise the case in one 

 example in the foot ; but, as in the theory which 1 propounded, there 

 should have been originally four germs in each interosseous space, 

 two dorsals coalescent into each bicipital muscle, and two palmars, of 

 which one is obsolete. These examples of Mr. Wood are only what we 

 might expect in case of the rudimental presence of a muscle embryo. 



21. The extensor secundi internodii pollicis longus of Blandin oc- 

 curred once during the last session in the form of a slip, arising from 

 the external condyle and fascia of the forearm, closely connected to the 

 extensor communis digitorum. It passed superficial to the ordinary 

 extensor of the second internode of the thumb, in common with which it 

 was inserted ; it traversed the third groove in the annular ligament, and 

 so was separated below from the tendon of the extensor communis digi- 

 torum. In the common otter a similar extensor tendon for the pollex 

 comes from the extensor communis. 



22. Two new instances of the brachio-fascialis have occurred with- 

 in the past session, but in no respect dissimilar to those already de- 

 scribed. One other third specimen arose from the coracoid process in 

 common with the short head of the biceps, from which it soon separated, 

 and formed the entire of the semilunar fascia. 



23. The flexor carpi radialis brevis seu profundus of Wood occurred 

 but once during the past year, co-existent with the palmaris longus. 

 This specimen was published by Mr. Wood (" Proceedings of the Eoyal 

 Society," 1867, p. 530), to which paper, and to another by the same 

 author in the " Journal of Anatomy and Physiology," vol. L, p. 55, I 

 would refer for fuller information on this muscle. 



