274 



MR. r. G. PARSONS ON THE 



[Mar. 20, 



Inierossei. — Thei'e are eight interossei, which all lie in the same 

 plane, rising from the semilunar cartilage and being inserted into 

 the eight sesamoid bones in front of the four metacarpo-phalangeal 

 joints. The most ulnar of these has already been described as the 

 flexor brevis minimi digiti. In Castor only six of these are present. 



Muscles of TrunJc. 



Pantiiculus Carnosits. — The panniculus is \^ell marked in 

 Rodents, and consists in many places of two or more layers of 

 fibres running in difierent directions. The superficial panniculus 

 in the neck rises from some of the face-muscles, more especially 

 the orbicularis oris, and runs back along the side of the neck to be 

 attached to the spine of the scapula ; it probably corresponds to the 

 human platysma. In Spermophilus, in which the cheek-pouches 

 are present, part of this muscle is specially developed, and runs 

 from the end of the pouch to the metacromial process. On the 

 ventral surface of the neck the fibres decussate across the middle 

 line, and run backwards and outwards over the pectoral region ; 

 as a rule, these decussating fibres are more or less scattered, but 

 in Octodon they are very well marked, rising from a small origin a 

 little to the side of the symphysis nienti, and spreading out in a 

 fan-shaped manner to cover the opposite side of the neck. Deep 

 to these fibres lies the sterno-facialis, which is attached to the 

 anterior part of the sternum and runs forwards to spread out over 

 the masseter, covering the sterno-mastoid in its course ; it is very 

 well marked in all the Octodontidae. 



Fig. 9. 



DEEP Plk>^M^CULU$ 



SUPEI^FICl*!. 



Panniculus of Octodon. 



The panniculus is not well marked on the dorsum of the neck, 

 but over the trunk it is found as a thick mass ; over the shoulders 



