ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 



343 



sp.sk: Anterior ) ^^^^necting processes of sp.sl: 

 sp.sfc" Median. ) 



ss. Slime sacs — numbered from before back- 

 wards. 

 sy. "Sympathetic" nerve, formed by the 

 fusion of the two RR. iutestinales vagi. 

 thy. Thyroid vesicle. 

 t.o. M. transversus oris. 

 t.p. M. tentacularis posterior. 



tr. "Trabecula." 

 ur.pp. Urinary papilla and apertures 

 vel. Pharyngeal velum. 

 v.q. Ventral division 

 v.q.' Middle division 

 v.q." Dorsal division 

 v.qt. Ventriculus quartus 

 v.s. M. velo-spinalis. 



of the M. velo-quad- 

 ratus. 



Plate I. 



Fig. L Median vertical longitudinal section of a 26-|-cm. Hag. x 8^. The drawing is necessarily based 

 on the study of a number of sections immediately about the median plane, and was originally sketched out 

 with Edinger's projection apparatus. Care has been taken to make it as accurate as possible. Visceral 

 cavities, shaded ; vascular spaces, red ; hard and soft cartilage, green ; pseudo-cartilage, obliquely striated. 

 The tentacles and nasal rings are numbered from before backwards, and the isolated spaces in the anterior 

 portion of the brain represent vestiges of the ventricular system. 



Fig. 2. Reconstruction from serial sections of the branchial apparatus of a 25-cm. Hag, seen from the 

 ventral surface, x 9|. The sliape of the third pair of gills is somewhat exaggerated owing to the fact 

 that the specimen had to be cut into three pieces to get it into the microtome, and one of the two breaks 

 was through this region. Gills, afferent and efferent ducts, and the external branchial apertures displayed 

 laterally, in order that all may be shown, but the position of all the structures in the longitudinal plane is, of 

 course, correctly indicated. Outer and inner surfaces of gills not differentiated. Ventral or cardiac aorta, 

 red. Afferent and efferent gill ducts numbered from before backwards. 



Plate II. 



Fig. 3. Reconstruction of the detached vesicules (251 in number) forming the thyroid gland of a 25-cm. 

 Hag, viewed laterally from the left side. x 11. For the reason mentioned above, the length of vesicle* is 

 somewhat exaggerated, which explains also the gap between sections 2560 and 2600. A few of the alveoli 

 are represented displaced vertically for the sake of clearness, but only occasionally do the vesicles overlap in 

 the transverse plane. Similarly the club-shaped muscle has been slightly depressed, so as not to overlap the 

 anterior vesicles. Afferent gill ducts numbered from before backwards. Cardiac aorta, red ; and afferent 

 branchial arteries shown cut off short. 



Fig. 4. Dissection from the ventral surface of the portal heart, gall bladder, and adjacent region of a 38-cm. 

 Hag. X 3. The two lobes of the liver, with the gall bladder, have been turned to the left and pinned down. 

 Hepatic ligament and cystic peritoneum (together with the proximal portion of the cystic vein) removed. 

 Intestine displaced slightly to the right. Heart removed. Arteries, cross-striated. 



Fig. 5. Dissection from the right side of the cloacal region of a 37-cm. Hag. x 4. Myotomes and slime 

 sacs numbered from before backwards, the former being also partly cut aM'ay. Segmental duct dissected clear 

 and displaced dorsally. Sphincter cloacse, and right wall of cloaca, body cavity, and abdominal pore removed. 



Plate III. 



Fig. 6. Simplified diagrammatic horizontal section of the Myxinoid gill. x 17. The number of gill 

 lamellae is greater than that shown. The upper part of the section represents the appearance of a tangential 

 section, the lower part that of a central section. Afferent arteries, blue ; efferent arteries, red ; water spaces, 

 shaded. 



Fig. 7. Section number 240 of the large series of a 25-cm. Hag. x 12^. This set of five sections 

 is intended to illustrate the relations of the anterior region of the gut. All were drawn with Edinger's 

 projection apparatus. As regards the skeleton, the sections should be compared with the charts accompanying 

 Part III. of this work. Muscles indicated by circles ; vascular spaces of whatever character, red ; cartilage, 

 green ; pseudo-cartilage, obliquely striated ; cavity of mouth and nasal tube, shaded. 



