SCHULTE, SET WHALE. 



niculus and can be followed to the lateral septum ventral to the transversarius, through which 

 it gains attachment to the transverse processes of the caudal vertebrae. A muscular slip from 

 the dorsal division passes at the lateral margin of the neuro-muscular foramen, intervening 

 between it and a weak area in the dorsal aponeurosis, to be inserted upon the ventral tendi- 

 nous expansion. Near this point of insertion, which is just caudal to the ischium, a small trans- 

 verse muscle arises and passing mesad is inserted into the fibrous tissue of the midventral line, 

 in common with its antimere, between the anus and the first chevron bone. It is possible to 

 see in this the representative of the coccygeus. 



The rectus is enclosed in a strong sheath derived from the aponeurosis of the obliqui and 

 transversalis. It is weak in the thoracic region and here adheres to the venter and dorsum 

 of the muscle so firmly as to be removed with difficulty. The aponeurosis of the external oblique 

 forms the more ventral layer of the sheath; that of the internal oblique splits to enclose the 

 rectus, and this cleft involves the muscular fasciculi as well as the aponeurotic lamellae, while 

 the aponeurosis of the transversalis forms the ental layer passing wholly upon the dorsum of 

 the rectus. These several layers fuse in the midventral line to form the linea alba, which is 

 narrow and weak in the thoracic region becoming firm and dense in the abdomen. At the 

 umbilicus the dorsal and ventral layers of the sheath are continuous around the mesal margin 

 of the rectus, and are separated from those of the opposite side by an interval which gives 

 passage to the umbilical cord. Here the connective tissue structures are very much thickened. 



The obliquus externus, except upon the front of the thorax, is an extremely thin sheet. 

 It arises by a series of digitations from all the ribs and beyond these from the lumbar aponeurosis, 

 but here only to a very small degree, so that a considerable portion of the internal oblique is 

 left exposed. The slip from the first rib is massive and is attached to its ectal surface as well 

 as its caudal border abutting upon the insertion of the scalenus anticus, from which however 

 it is clearly separated. The remaining digitations are attached to the caudal margins of the 

 ribs at successively greater distances from the median line. Those arising from the second, 

 third and fourth ribs interdigitate with the scalenus medius, but I could not find that any fasci- 

 culi were continuous from one muscle to the other as Carte and MacAlister observed in B. 

 rostrata ( = B. acuto-rostrata). The slips from the fifth and sixth ribs interlock with slips of the 

 serratus anticus. The fasciculi are directed very obliquely caudad and mesad. They are 

 continued a short distance upon the venter of the rectus before becoming aponeurotic, except 

 at the caudal end of the muscle where they terminate before reaching the rectus. 



The obliquus internus is considerably thicker than the externus. It arises from the lum- 

 bar aponeurosis as far caudad as the transverse plane of the vulva. Its fasciculi are directed 

 very obliquely rostrad and ventrad. At the margin of the rectus it divides into two lamellae. 

 The superficial promptly becomes aponeurotic and is thus inserted into the linea alba. The 

 more caudal of the fasciculi of the deep lamella behave in a similar manner upon the dorsum 

 of the rectus muscle, the more rostral are inserted upon the caudal margins of the cartilages of 

 the last seven ribs, close to the slips of origin of the rectus. 



The transversalis, arising likewise from the lumbar aponeurosis and for about the same 

 extent as the obliquus internus, is directed transversely towards the median line, its aponeuro- 

 sis passing wholly dorsal to the rectus. The sheet is continued in the thoracic region by slips 

 from the deep surface of the extremities of the last nine ribs, interdigitating with the origins of 

 the diaphragm. Like the external oblique this layer is very thin. 



