742 MR FRANK J. COLE 



him. The last twelve myotomes often exhibit a gradual simplification of this 

 pattern, so that the last few septa appear as sinuous vertical lines. In other specimens, 

 however, as shown in fig. 4, the pattern may be continued practically to the very 

 extremity of the tail. The last myotome is a very small, irregular, and variable patch 

 of longitudinal fibres at the tip of the tail. The slime sacks behind the cloaca, as 

 described below, are partly covered dorsally by the myotomes. 



The first myotome, i.e. of the small type, lies largely between the anterior dorsal 

 extension of the obliquus and the copulo-palatinus, and arises from the fascia between 

 these muscles. The succeeding myotomes, except those behind the cloaca, are all 

 covered ventrally by the obliquus, but the dorsal and greater portions are seen at once 

 on removal of the skin. The second, third, fourth, and fifth myotomes are thin dorsally, 

 and roof over the membranous brain case, being closely attached to it. The anterior 

 myotomes are also attached to the posterior extremity of the anterior process of the 

 pterygo-quadrate, the superior and (the anterior end of) the inferior processes of the 

 same, the auditory capsule, the dorsal portion of the hyoid arch, and the anterior end 

 of the superior lateral cartilage. Below, the anterior myotomes cover the muscles of 

 the head, pharynx, and the so-called " club-shaped muscle." Behind the fifth myotome 

 the parietalis gradually thickens dorsally, where for the remainder of its length it is 

 very fleshy, and attached to the roof and sides of the neural tube and the lateral 

 surface of the chorda, from thence becoming thinner as it passes ventrally. From about 

 the seventh to the twenty -third myotome a wide interval is left dorsally between the 

 parietalis and the club-shaped muscle, in which space course the very diffuse second 

 and third divisions of the constrictor pharyngis. This hiatus is directly continuous 

 with the very large extra-branchial space, and the corresponding one at the dorsal 

 region of the heart, abdomen, and tail, and is everywhere traversed by the silky adipose 

 areolar tissue supporting nerves and blood-vessels. At the gill and cardiac regions the 

 parietalis, together with the notochord, forms the lateral walls and roof of this space, 

 whilst below it is bounded by the obliquus and rectus muscles. The parietalis, however, 

 reaches its greatest development in the abdominal region. Here the muscles of the 

 two sides are separated at the mid-dorsal line by a thin vertico-longitudinal partition 

 arising from the roof of the neural tube. From thence the muscle extends downwards 

 as a rapidly thickening mass at the side of the neural tube and chorda, being closely 

 attached to these, and attaining its greatest thickness opposite the ventral surface of 

 the latter (fig. 1). Here, with the chorda, it forms the roof of the abdominal tube. 

 It now extends downwards, becoming gradually thinner, in order to terminate in a 

 free border immediately over the slime sacks, and being only separated from the latter 

 by the obliquus muscle. Here also it forms the lateral wall of the abdominal tube 



On the tail, where of course there is no body cavity nor any obliquus or rectus 

 muscles, and where, apart from the transversus caudalis and the cordis caudalis, there 

 is no other muscle present, there is a relatively greater development of the parietalis 



