406 THE ZOOLOGIST. 
averages from three to four inches in length in a relaxed condition, 
and nearly half an inch in diameter. Its posterior extremity is 
provided with two large, soft, diverging and erectile bulbs, the 
erectile tissue of which extends through the whole length of the 
corpora cavernosa. 
The peritoneal canals, which in other species penetrate nearly 
to the male organ, in the Aspidonectes do not reach one-third the 
length of it. The testes seem disproportionately large in smaller 
individuals, those of a reptile scarcely nine inches in length 
equalling those of a specimen fully fourteen inches over all. They 
measured one and one half inches in length, by from one-fourth to 
to one-third of an inch in thickness, having the elongated form of 
the organs of pennibranchiate reptiles rather than the round one 
common to the Testudinale. Both the epididymis and the 
vas-deferens are very long and convoluted. 
Of the peculiarities of the muscular system, those of the 
retractors of the neck present the most interesting differences. 
Cuvier describes the retrahens capitis et colli as arising by its 
longer part from the ribs of the fifth and sixth dorsal vertebra, 
within the carapace, and, passing in the interval between the lungs 
on the sides of the anterior part of the neck, is inserted by means 
of fasciculi to the transverse apophyses of the third, fourth, and 
fifth cervical vertebra, the long fasciculus passing to the head to 
be inserted on the basilar process of the occipital bone; the shorter 
portion, arising from the fourth and fifth dorsal vertebra beneath 
the articulation passes for insertion into the side of the sixth 
cervical. But in the Aspidonectes the retrahens cervicis is a 
single muscle on the side of the neck, and at the anterior attach- 
ment, but in its posterior insertion becomes a triceps. Attached to 
the side of the first cervical vertebra it follows by its side to the 
thorax, where it divides into three separate portions, which, how- 
ever, remain side by side in the anterior part of the cavity and 
between the lungs, there dividing, one part passing back alongside 
the vertebral column, through the pelvis, to be inserted into the 
posterior portion of the fourth caudal vertebre; the other two 
portions diverge laterally, one being inserted into the intercostal 
space of the sixth and seventh ribs, and the other into the outer 
part of the like space of the seventh and eighth. This muscle 
replaces the vretrahens capitis collique described by Ludwig 
Heinrich Bojanus. 
