SCHULTE, SEI WHALE. 427 



farther laterad upon the latter as it proceeds rostrad, and making fibrous arches over the lumbar 

 vessels, beside the vertebral bodies. The lateral tract is situated between the foregoing and the 

 transversarius. At the beginning of the pedicle it arises from the sides of the vertebrae, receiving 

 also a tendon of origin from the great tendon of the mesal tract. It enlarges rostrad deriving 

 fleshy fasciculi from the sides of the vertebrse, and in addition receives seven tendons of origin 

 from the interval between it and the transversarius. These arise from the bodies of the ver- 

 tebrae and are at first incorporated in the intermuscular septum, their line of origin extending 

 rostrad about half the length of the pedicle. They are directed mesad as well as rostrad passing 

 superficial to the fleshy belly of the lateral tract until they come to lie beside the great tendon 

 of the mesal tract. They end in fleshy bundles which are added to the mesal aspect of the 

 lateral tract. As it is followed rostrad this portion of the muscle comes more and more to overlie 

 the mesal tract, with which in the lower abdomen it becomes inextricably blended. The fas- 

 ciculi of both tracts, while in general longitudinal, have an inclination laterad, passing from 

 mesal origin to lateral insertion, exception made of the vertebral insertions already mentioned, 

 which belong to the mesal tract. In the pedicle the whole muscle including its tendons is cov- 

 ered by a dense aponeurosis which is attached mesad to the extremities of the chevron bones, 

 and laterad to the septum between it and the transversarius. From the first chevron rostrad 

 this becomes replaced by a muscular layer which ensheaths the longitudinal tracts and their 

 tendons, its own fasciculi having a more oblique direction. On its deep surface it is closely joined 

 to the rest of the muscle by exchange of fasciculi. 



The insertion is into the bodies of the abdominal vertebrae as far rostrad as the first lumbar, 

 into the ventral surfaces of their transverse processes to a degree which increases rostrad, into 

 the caudal border and ental surface of the last rib in its whole length, and into the ental surfaces 

 .of the twelfth and eleventh ribs in the region of their angles. It is innervated by branches of 

 the lumbar nerves as they pass obliquely through its substance. 



Dorsal musculature. In the description of these muscles I have used the terminology and 

 classification of the human anatomists, following Eisler 1 as closely as the nature of the case 

 permitted. I have made but few references to the literature of cetacean myology, because 

 this is almost confined to the Odontoceti and has been summarized by Leche, 2 while Carte and 

 MacAlister's account of Balcenoptera is too abbreviated and incomplete to be of much assistance. 

 I have therefore limited myself to memoranda of the conditions observed, and here have sought 

 to describe the general relations and extent of the several systems rather than to enter upon their 

 structure in detail, for which the small size of this foetus makes it rather unfavorable material. 



Spino-costal muscles. This layer is very rudimentary as it is for the most part repre- 

 sented by a fascial layer. The serratus posticus inferior is very thin and its fasciculi insert upon 

 the 6th, 7th and 8th ribs near their angles. It is covered by the latissimus dorsi. I failed to 

 find a serratus posticus superior. Neither are mentioned by Carte and MacAlister. 



Spino-dorsal muscles. These muscles are of enormous size and for the most part so inti- 

 mately connected by exchange of bundles, that their resolution into tracts is more than usually 

 difficult and at best schematic. An exception is present in the transversarius, which in its whole 

 length is separated from the other spinodorsal muscles by a definite septum. From this mesad 



1 Eisler, P. Die Muskeln des Stammes, in Bardeleben's Hanb. der Anat. des Mensch. Jena, 1912. See also Henle, Anat. des 

 Menschen. Braunschweig, 1873. 



- Braun's Thierrcich, Siiugethiere. 



