450 NERVOUS SYSTEM AND SENSE ORGANS OF AJIIURUS. 



PLATE IV.— {Continued). 



CI., claustrum. S., 'stapes.' 2, 3, 4, dorsal roots of 2nd, 3rd and 

 4th spinal nerves with their respective ganglia. 1 the position of 

 the first spinal ganglion which does not appear in this section. 

 A 3 ., the arch of the 3rd vertebra. Ms., medulla spinalis. Ap., 

 Ampulla frontalis. 



Fig. 12. — Th.. thymus. Lb., most posterior of the levatores 

 branchiarum. R. lat. vag., points to the root of the vagus in con- 

 nection with which is seen the portion of the ganglion trunci 

 which gives off the ramus lateralis. Si., sinus impar. or saccus 

 endolymphaticus. Csi., in the cavum sinus imparis pointing to the 

 osseous lateral wall of the cavum. i., the 'incus.' m., the 

 'malleus.' Asi., points to the atrium sinus imparis, as bounded 

 by the spoon-shaped process of the ' stapes ' s. , and lies on the 

 thickened patch of dura mater which is seen in vertical section 

 in Fig. 14. I., II., III., IV., stand on the middle points of the 

 centra of the 1st, 2nd, 3rd and 4th vertebras. Ab., in the cavity 

 of the air-bladder points to its union with the posterior end of the 

 malleus. Vcid. , vena cava inferior dextra. 



Fig. 13. — Gc, the gill cavity and its opening on the left side. 

 EGc, epithelium of the roof of the gill cavity. De., duct, endo- 

 lymph. As., asteriscus in the lag. cochlear. Csi., in the cavum 

 sinus imparis points to the basi-occipital and the exoccipital cartil- 

 ages resting on it. G. IX. & X., ganglia of glossopharyngeus and 

 vagus. 

 Figs. 14 and 15, are from vertical sections through fish of same age as the 

 foregoing horizontal sections, of which 15 is the more anterior. 



(E ., oesophagus. Mc, mucous canal in postfrontal. R. lat. V., 

 ram. lateralis trigeinini. Cp., canalis frontalis. Lc, lagena 

 cochlear. *S'., sacculus. Ao., aortas at sides of which are the 

 sympathetic ganglia, The sections are slightly oblique, so that the 

 right sides represent planes somewhat posterior to the left. The 

 thymus is seen on the one in continuity with the epithelium of the 

 gill cavity, on the other its posterior end is seen wedged in between 

 the trapezius muscle and the levat. branch, post. 



Additional letters in 14. 



Lc, lateral mucous canal in section. Hk., head-kidney. L., 

 liver. R. lat. va., ram. lat. vagi in section as it crosses the 

 transverse portion of the supraclavicle. Bo., Basioccipital. 0c, 

 occipital cart., above which is the supraoccipital spine. D.M., 

 dorsal musculature attached to the posterior surface of the skull 

 on either side of the foramen magnum. 



For additional lettering, see foregoing figures. 

 FiG-s. 16, 17, 18.— The otoliths, sagitta, asteriscus and lapillus, x 6. 



