REPORT ON THE MARSUPIALIA. 97 



Veterinary anatomists rightly term these muscles " interossei," but they are in error, 

 in so far that they consider them to be the interossei of the lateral digits, i.e., the first 

 and fourth dorsal interossei. These muscles have undoubtedly disappeared along with the 

 digits to which they belonged. 1 



Bovidce (Oxen). 



In the Ox the two digits which are present represent the medius and annularis. 

 The metatarsals corresponding to these toes are fused so as to constitute a single 

 bone, the double constitution of which is marked (1) by a deep longitudinal furrow 

 on its anterior surface, (2) by a slightly marked groove on its posterior aspect, 

 and (3) by a notch on its inferior extremity which separates the two articular surfaces. 



The suspensory ligament of the Ox shows its muscular origin in a still more striking 

 manner than that of the Horse. It is an exceedingly powerful structure which rests 

 upon the posterior face of the metatarsus ; expanding somewhat as it descends, it divides 

 opposite the junction of the middle and lower thirds of the fused metatarsal bones into 

 five distinct portions ; of these (1) two go to the annularis ; (2) two to the medius ; and 

 (3) one passes forwards in the notch which separates the two articular surfaces on the 

 lower end of the metatarsus. The slips which go to the digits, have in each instance 

 precisely the same insertion. They are inserted one into each of the sesamoid bones at 

 the base of the first phalanx, whdst the marginal slip on each side sends forwards a 

 strong flat band to be attached to the extensor tendon on the dorsum of the first 

 phalanx of the corresponding toe. The remaining slip which passes forwards is central 

 in position, and it reaches the dorsum of the foot in the interval between the two first 

 phalanges of the digits. Here it splits into two diverging portions which join the extensor 

 tendons on the dorsal aspect of the toes. 



The suspensory ligament has thus two distinct insertions on each side of each digit, 

 viz., into the sesamoid and into the extensor tendon, and in this manner an extremely 

 powerful brace is formed, which very efficiently prevents over-extension at the metatarso- 

 phalangeal joints. 



But this ligament has also two additional attachments of an altogether different 

 nature. From the middle of its superficial or posterior surface, two thick rounded 

 tendinous looking slips arise. These pass downwards and, joining the tendons of the 

 perforatus, take part in the formation of the double ring through which the two tendons 

 of the perforans pass. 



1 We may at this stage refer to the foot of the Tapir. In Dr. Murie's admirable paper upon the Malayan Species 

 (Jour. Anat. and Phys., vol. p. 166) the intrinsic pedal muscles are described and figured so clearl}- that although he 

 speaks of them simply as single and double interossei, there is no difficulty in recognising their homologies. In this 

 foot the hallux and minimus are absent. The plantar layer is composed of two muscles, viz., (1) the adductor indicis, 

 and (2) adductor annularis. The intermediate layer consists of a strongly marked two-headed flexor brevis appro- 

 priated to each digit. No members of the dorsal layer are present, but it is very probable that they have fused with 

 the strongly marked short flexors. 



(ZOOL. CHALL. EXP. — PART XVI. — 1882.) Q 13 



