368 DISCOVERY REPORTS 



MUSCULATURE 



An excellent account of the general musculature of the region has been given by 

 Schulte (19 1 6), who described a foetal Sei whale (Balaenoptera borealis), and it is not 

 intended here to do more than give a brief outline of the main muscles based on 

 Schulte 's account. 



The panniculus carnosus is a thin sheet of muscle fibres belonging to the dermal 

 series, extending over the whole anterior and middle part of the body beneath the blubber 

 layer, but forming a fibrous sheath upon the pedicle behind the anus. The pannicular 

 layer is thickest and most pronounced in the ventral abdominal region and over the 

 cavum ventrale. A latero-dorsal aponeurosis towards which the fibres of the panniculus 

 are directed divides them into a ventral and a dorsal series. The fibres of the dorsal 

 series are directed almost vertically downwards towards this aponeurosis, while those of 

 the ventral series pass upwards somewhat more rostrally from their origin in the mid- 

 ventral line. Around the umbilicus the origins of the ventral series on each side 

 separate, leaving a gap which admits the structures of the umbilical cord. The 

 panniculus is not continued on to the umbilical cord itself. Immediately in front of 

 the base of the penis the panniculus forms a thick muscular mass which is continued on 

 to the organ and forms a muscular sheath in its proximal extremity. This mass is 

 interposed anteriorly between the base of the penis and the rectus abdominis muscle. 



The obliquus internus muscle is a fair-sized sheet with rostro-ventrally directed fibres 

 arising in the lumbar region from the latero-dorsal aponeurosis already mentioned. 

 At the dorsal margin of the rectus abdominis the obliquus internus divides into two 

 sheets. These become fibrous and form a sheath for the rectus. The superficial sheet 

 is inserted upon the linea alba, and the deep layer is aponeurotic upon the sheath of the 

 rectus muscle internally. The more rostral fibres of the deep layer are inserted upon the 

 caudal margins of the cartilages of the last seven ribs close to the slips of origin of the 

 rectus (Schulte). 



In its central and caudal portions at any rate, the rectus abdominis is thus enclosed 

 in a fibrous sheath derived from the forking into two layers of the obliquus internus. 

 Schulte states that dorsally the aponeurosis of the transversalis (a thin horizontally 

 directed sheet dorsal to the rectus) is concerned in the formation of this sheath. 



The rectus abdominis forms a thick mass on the venter of the abdomen, the fibres 

 running rostro-caudally. The linea alba, formed in the mid-ventral line by the fusion 

 of the sheaths of the recti of the two sides, separates the rectus muscle of each side from 

 its antimere. At the umbilicus the two muscle masses diverge to admit the cord so that 

 the muscle fibres are not continued upon it. In the posterior part of the abdomen, 

 immediately in front of the penis (or vulva in the female), the separation of the recti 

 of the two sides becomes very pronounced and a triangular gap is left filled with fibrous 

 tissue and roofed, ventrally, by a thick muscle mass derived from the panniculus. 

 Lateral to the inguinal region the rectus has three terminal insertions. The smallest and 



