234 OF URCHINS IN GENERAL. 



and intermaxillary bones. Another pair of muscles 

 arises from the posterior extremity of the oval. 

 They are of a broad pyramidal form, and are like- 

 wise continued with the external orbicular fibres. 

 The tendinous point of each is inserted laterally 

 near the end of the tail. There are also two other 

 sub-cutaneous muscles, situated towards the belly, or 

 below the great orbicular muscle. 



" When the skin of the belly is removed, we 

 readily perceive three distinct portions of fleshy 

 fibres. The first is situated under the throat, and 

 corresponds to the cutaneus colli. It comes from 

 the top of the breast, under the skin, and is in- 

 serted . on the lateral parts of the head, near the 

 ears. The portion of one side unites to its cor- 

 respondent by a middle line, which is composed of 

 fat. The second comes from the middle line of 

 the sternum ; it takes an oblique direction, becom- 

 ing thicker and narrower above the shoulders, as it 

 proceeds to join the edge of the great orbicular 

 muscle. The third ventral portion, which is still 

 more slender than the two former, extends over 

 the whole surface of the abdomen; it arises from 

 the circumference of the arms, from the lateral 

 parts of the tail, and from the tops of the thighs: 

 upon reaching the ribs it divides. The internal 

 portion, which is .the broader of the two, passes 

 under the arm-pi^ and is inserted into the upper 

 part of the os humeri. The external portion is 



prolonged 



