ON THE GENERAL MORPHOLOGY OF THE MYX1NOJD FISHES. 



755 



mes. Median dorsal mesentery transmitting a 



genito-mesenteric artery. 

 nas. M. nasalis. 

 obi. M. obliqims. 

 obi'. Terminal post-cloacal section of the M. 



obliquus. 

 ov. Ovarian portion of the hermaphrodite 

 gonad. 

 par. M. parietalis (forming the myotomes). 

 p. e. p. M. palato-ethmoidalis profundus. 

 p. e. s. M. palato-ethmoidalis superficialis. 

 pi. c. External head of the M. palato-coronarius. 

 pp. M. perpendicularis. 

 pt. Peritoneum. 

 p. v. Portal vein, receiving vessels from the gut 



and the gonad. 

 q. p. M. quadrato-palatinus. 

 r. d. R. dorsalis of the spinal nerve. 

 red. M. rectus. 



r. v. R. ventralis of the spinal nerve. 

 s. ao. Systemic aorta. 

 sc. b. s. Subcutaneous blood sinus. 

 s. cl. M. sphincter cloacae. 



v. e. 



s. d. Segmental duct. On the right side is 

 shown a Malpighian body opening into 

 it, with its arterial and venous supply, 

 s. s. Slime sack. On the right side of fig. 1 



is shown a duct and its aperture. 

 s. s. Depressions on the M. obliquus seen on 

 removal of the slime sacks. 

 sy. Sympathetic nerve or R. intestinalis, 

 formed by the fusion of the two visceral 

 branches of the vagus. 

 t. c. M. transversus caudalis. 

 t. e. M. tentaculo-ethmoidalis. 

 t. o. M. transversus oris. 

 t. p. M. tentacularis posterior. 

 m. s. Middle and superior cutaneous vein. 

 v. q. Ventral division"! 



v. q. Middle division r of the M. velo-quadratus. 

 v. q". Dorsal division J 

 v. r. Ventral root of the spinal nerve formed 



by the fusion of four rootlets. 

 v. s. M. velo-spinalis. 

 v. sp. Spinalis vein formed by the union of 

 superior and inferior spinal veins. 



Plate I. 



Fig. 1. Diagram illustrating the anatomy of a typical body segment of Myxine, reconstructed from 

 various series of sections. Although all the structures which may occur in one segment have been projected 

 into the same plane, the relative positions of the same are correctly indicated as found in a 19 "5 cm. Hag. 

 On the left side the distribution of a spinal nerve is shown in black, and on the right side the course of a 

 segmental artery and vein in red and blue. On the right side the subcutaneous space, otherwise continuous 

 round the body, is interrupted by the opening of the slime gland. It must be understood that the diagram 

 epitomises the possibilities of a segment, and not the actual structure of every somite. 



Plate II. 



Fig. 2. Reconstruction from the large series of sections of the 25 cm. Hag of the M. constrictor 

 branchiarum et cardiae of the left side, x 11. The muscle is coloured red and its lacunae black. The 

 shape of the third gill is somewhat distorted, owing to the fact that the specimen had to be cut into three 

 pieces in order to get it into the microtome, and one break was through the third gill. When the tissues are 

 cut before embedding some swell more than others and project beyond the cut surface, and this disturbs the 

 enumeration of the sections. For the explanation of the numbers, refer to the description of the muscle 

 based on the sections in the text. 



Fig. 3. Dissection from the left side of a 34| cm. Hag, to illustrate the superficial anatomy of the muscles 

 of the head and branchial region. x 3. The following structures have been removed : M. tentacularis 

 posterior ; the myotomes (except dorsally in front of the gill region) ; M. rectus (except insertion and a 

 detached portion at the level of the first gill) ; M. obliquus ; greater portion of the continuous external 

 posterior sheet of the M. constrictor branchiarum et cardiae ; efferent gill ducts and the ductus cesophago- 

 cutaneus (position of latter indicated by its constrictor — 14) ', heart and left anterior cardinal and inferior 

 jugular veins. Tentacles 3 and 4 cut off. Tentacles, gill sacks, and the regions of the M. constrictor 

 branchiarum et cardiae indicated by numerals (cp. text). Soft cartilage, blue ; hard cartilage, red. Arteries, 

 red and cross-striated ; nerves, black. 



TRANS. ROY. SOC EDIN., VOL. XLV PART III. (NO. 26). 107 



