xxiv Journal of Comparative Neurology. 



first of these contributions appeared in Vol. XXIV, 1896, and included 

 the following parts: I, Gastrulation ; II, the Anlage of the middle 

 Germ Layer and Chorda; III, The Anterior Head Somites; IV, Ol- 

 factory Organ; V, Mouth and Hypophysis. The second article, in 

 Vol. XXV, 1897, includes : VI, the 4th and 5th pahngenetic Head 

 Somites; VII, the 6th palingenetic .and the 4 cenogetic or occipital 

 Somites; VIII, Ventral Nerve Roots of the Head Somites; IX, De- 

 velopment of the IV Nerve. The third article appeared in Vol. 

 XXVII and contains part X, Development of the Dorsal Nerve Roots 

 of the Head Somites. 



Hoffmann supports the general view that both sensory and motor 

 roots of the nerves of the branchial type correspond to dorsal roots, 

 these segments lacking ventral roots. All post-vagal motor roots, how- 

 ever, represent ventral roots of nerves of the spinal type, and the 

 same is true of the VI and III nerves ; but the IV nerve he 

 regards as a dorsal nerve. It belongs with the same segment as a por- 

 tion of the trigminus. In fact, the trochlearis and the portio trigemini 

 rami ophthalmici superficialis are one and the same nerve. They sep- 

 arate only in late embryonic stages and there is always a fibrous con- 

 nection between them in the adult, as Schwalbe has described. 



The branchiomeric nerve is regarded as a dorsal nerve. Its typical 

 composition in selachians includes a dorsal ramus and a ventral ramus. 

 The latter gives off (i) the r. post-trematicus, of mixed sensory and 

 motor function and regarded as the continuation of the trunk of the 

 nerve; (2) the r. pro-trematicus, wholly sensory; (3) the r. pharyn- 

 geus, wholly sensor}-. 



The trigeminus and facialis are both regarded as double, or dimet- 

 americ, nerves, the former divisible into the " thalamo-ophthalmicus " 

 and the " trochleo-trigeminus," and the latter into the " ophthalmico- 

 buccahs " and the " acustico-hyoideo-mandibularis." The author's 

 scheme of the primitive metamerism of Acanthias is somewhat as 

 follows : The ventral nerve of the first somite (excluding the anterior 

 head cavity of Miss Piatt) is the oculomotorius, its dorsal nerve the 

 " thalamo-ophthalmicus," or profundus, or thalamicus nerve. In early 

 stages its ganglion is distinct, viz., the g. ciliare of Van Wijhe, the g. 

 mesocephali of Beard. Hoffmann calls it the g. ophthalmici. It fuses 

 with the skin and third nerve, then separates from the skin and with- 

 draws from the oculomotorius, but retains fibrous connection with the 

 latter, and grows toward the trigeminus ganglion (of the next follow- 

 ing segment), finally fusing with it. A ciliary ganglion belonging to 

 sympathetic system appears more distally on the third nerve and con- 



