Parker and Rico—Ox the Myology of Patinurus Edwardsti, Hutton. 165 
abdominal muscles. In the second segment the slip from the enveloping muscle of 
the preceding segment is absent. In the fifth and sixth segments the three factors 
are so closely united as to form a single band. 
In the third, fourth and fifth segments the longitudinal flexor is reinforeed by a 
narrow slip springing from the mesial aspect of the central muscle of the segment 
next in front: this may be called the zxz¢ernal accessory longitudinal flexor. 
In the third and fourth segments there is also an external accessory longitudinal 
flexor arising from the central muscle of the segment next but one in front, and 
inserted with the external flexor into the sternal aponeurosis. 
The telson is depressed by a single muscle on each side, which arises from the 
fifth sternum and sends off a lateral slip to the basipodite of the sixth abdominal 
appendage. It lies dorsad of the flexor muscles of the lateral tail-lobes. 
Thus any typical abdominal segment, such as the third, is acted upon by the 
following muscles :— 
foo) 
1. A pair of saperficral extensors, situated in the segment next in front and 
inserted into the anterior border of the tergum near the middle line. 
2. A pair of deep extensors, situated in the segment next in front, beneath the 
preceding, and inserted into the anterior border of the tergum near the middle line. 
3. A pair of oblique extensors, derived mainly from the central muscle of the 
segment itself but partly also from that of the preceding segment, and inserted into 
the terguin immediately above the peg-and-socket joint. 
4. A pair of accessory oblique extensors, arising from the transverse muscle of the 
segment itself. 
5. A pair of superficial flexors, situated in the segment next in front and inserted 
into the sternum a short distance from the middle line. 
6. A pair of longitudinal flexors, arising from the inner limbs of the enveloping 
muscles of the segment next but one in front and inserted into the sternum near the 
middle line. 
7. A pair of external accessory longitudinal flexors, arising from the central muscle 
of the segment next in front and inserted with the preceding. 
8. A pair of external flexors, arising from the outer limbs of the enveloping 
muscles of the segment next behind and joining the insertions of the longitudinal 
flexors by an aponeurotic band. 
