318 Dr. A. Macalister on the Formation of 



the uniformity of development of the typical muscle-germs dis- 

 tinctly traceable. It must at once be noticed that the inter- 

 ossei of the human hand and human foot do not correspond, 

 but differ strikingly in respect to their line of action — those of 

 the manus working to and from the line of the middle finger, 

 those of the pes having a similar relation to the second toe. 

 In the pes of the chimpanzee, Humphry has found them ar- 

 ranged in the same way as we find in the himian manus. In 

 the gorilla, Duvemoy and Halford found them to be arranged 

 in the same manner ; and the latter anatomist has met with 

 the same arrangement in Macacus. I have examined them in 

 Cercopithecus^ Macacus, Rhesus ^ and Cynocephalus] and Mivart 

 has examined the first-named genus, and found them alike. 

 Prof. Humphry has dissected them in the dog, and has found 

 the same arrangement, which I have likewise confirmed, in a 

 dingo. In the manus of Dasyims I have found them arranged 

 thus : — the fifth digit had an internal interosseus from the 

 carpus to the first phalanx ; the fourth had none ; the third had 

 a fasciculus attached to its ulnar side; the second had a special 

 one to its radial side ; and the pollex had one to each side. 

 Thus we see another instance of a variation from the true 

 manus type. But it is in Ornithorhynchus, Hyrax^ and Nyc- 

 ticebus that these attain their greatest degree of complexity. 

 In the first named a regular double set of muscles occupy the 

 interosseous spaces, one for each side of each finger. In Hyrax 

 there are two sets of interosseals : — first, a regular set, one at 

 each side of each finger, and inserted into the sesamoid bones 

 at the base of the first phalanges ; secondly, a group of longer 

 muscles — one an external muscle for the index, two external 

 parallel muscles for the annularis, and one for the little finger, 

 supplemented by an abductor minimi digiti. In the foot of 

 this animal there are internal and external muscles for the 

 index, middle, and fom-th toes, an external muscle for the third, 

 and of the longer series an inner tendon for the third, and ex- 

 ternal muscles for the second and first. The Nycticehus like- 

 wise possesses a complex group of interossei as well as of 

 lumbricales, as in its manus are found an abductor and flexor 

 brevis pollicis, external and internal interossei for the index, 

 middle, annular, and little digits, supplemented by a special 

 abductor of the latter and by a transversus pedis consisting of 

 two slips, one springing from the second and the other from 

 the third metacarpal bone. The rat and hare possess four pairs, 

 as also does the rabbit ; while the guineapig and Agouti ex- 

 hibit three pairs of interossei. 



In deducing from these apparently dissimilar series a regular 

 typical form we see that the entire difficulty may be set at rest 



