MYOLOGY OF THE ORNITHORHYNCHUS . 157 



becomes a pure extensor of the little toe) for its posterior antitype. 

 We hold that the digital extensors of both members are, like the 

 flexor sets, essentially two, a deep, or "long," " perforans," and a 

 superficial, or "short," or "perforatus." Extensor minimi digiti 

 mauns, and extensor longus hallucis pedis are differentiations from 

 one set, and mutually antitypic ; while extensor indicis, and extensors 

 of the pollical internodes, are representatives of the other set, cor- 

 responding to the short extensor that remains upon the instep in the 

 human subject, but which, as in the opossum, may be carried up the 

 leg as one of the peroneal group. "Peroneus tertius " is another of 

 the same group, corresponding with extensor ossis metacarpi pollicis. 

 We recur to the subject again in speaking of foot muscles. 



(b'. — From carpo-metacarpus.) 



There are no digital muscles, except the dorsal interossei, arising 

 from the back of the hand ; on the contrary, several are found upon 

 the palm, among them the flexor digitorum perforatus, as well as 

 the short special thenar and hypothenar muscles, the lumbricales, 

 and palmar interossei. 



Flexor digitorum sublimis s. ])erforatus. — This muscle lies wholly 

 in the palm, as the corresponding " short" flexor of the toes of man 

 does in the sole ; and, like the same muscle of, for instance, the opos- 

 sum's foot, it arises upon and from the common tendon of the " long " 

 or profound flexor digitorum. It is a small muscle, in some danger of 

 being overlooked without due care ; but its tendons may be demon- 

 strated to have the essential characters and relations of those of a 

 perforatus set in the customary exhibition of the latter as a muscle 

 of the foi'earm. It arises as a flat fleshy mass upon the palmar (su- 

 perficial) aspect of the conjoined tendon of the deep fiexor, and 

 speedily splits into fascicles that terminate in delicate tendons that 

 pass to the bases of the fingers, and are mostly inserted into the ten- 

 dons of the deep flexor a little beyond ; but the tendons also spread 

 like two " pei'foratus " tendons, into an expansion joining the digital 

 sheaths, on either side of tendons of the deep flexor, which are thus 

 embraced in the usual way. 



Lumbricales. — Four of the five tendons of the deep flexor muscle are 

 accompanied and reinforced by four accessory muscles, that arise from 

 the dorsal (interior) aspect of the conjoined tendon before it splits, 

 and pass to be inserted as usual into the digital sheaths at the sides of 

 the fingers. 



Thenar and hypothenar muscles. — These are nearly alike, of small 

 size, and not dissimilar in general aspect to interossei; but their 

 mode of insertion exposes their character. The short special flexor 

 of the thumb is a small, flat fasciculus arising pretty definitely from 

 the most prominent carpal bone on the radial side, lying along the 



