George L. Streeter 21 



The (ominissnml group is made up of a compact group of small 

 intensel3^-staining multipolar cells, which are found in the grey com- 

 inissure in the thoracic division of the cord, from the 20th to 27th seg- 

 ments. It suggests, by its position, a possible relation with the viscera. 



The dorsal group includes in sections through the 26th to 31st seg- 

 ments a small group of cells on the median border of the grey matter 

 at the junction of the two dorsal horns. The cells of this group resemble 

 tliose of the lateral group, though slightly smaller. From their similarity, 

 in position and appearance, to the group in the mammalian cord these are 

 classed as Clarke cells (see Fig. 6, segm. XXIX). Otherwise as. note- 

 worthy are classed under the dorsal group the occasional small multi- 

 polar or spindle-shaped cells, which are seen on the periphery of the 

 dorsal horn both median and lateral, and frequently on the tip of the 

 horn near the entrance of the dorsal root. 



Peripheral Group. 

 In 1889 Lachi^" described a peripheral group of nerve-cells forming a 

 series of segmental projecting nuclei, occurring in the lumbo-sacral 

 enlargement of the spinal cord of doves. This nucleus was seen later 

 by Gaslell and Schafer but attracted little attention until KdUiker" 

 originally unaware of Lachi's work, published the results of a most 

 complete study of this structure, both in the embryo and the adult bird. 

 Kolliker finds three varieties of peripheral cell-groups, namely: Hof- 

 mann'sche Grosskerne, so named after his Praparator P. Hofmann, who 

 had called his attention to them; Hofmann'sche Kleinkerne; and a 

 scattered group. 



In the embryonal cord, 41/2- to 5-day chick, Kolliker describes a group of 

 cells separating itself from the superficial cells of the ventral horn. This 

 group in the 10-day chick is completely separated and forms a definite peri- 

 pheral nucleus, the Hofmann'sche Kerne. There are 28 of these nuclei on 

 each side of the cord, segmentally arranged according to the 28 spinal nerves 

 and ganglia. Of these nuclei the 5 or 6 pairs, corresponding to the level of 

 the sinus rhomboideus, undergo a marked development, and in the 15-day 

 chick can be seen bulging from the periphery of the cord just dorsal to the 

 ventral nerve roots, Hofmann'sche Grosskerne. The nuclei in the other 

 regions of the cord do not share this development, but remain more or less 



'" P. Lachi, Alcune particolarita anatomische del ringonfiamento sacrale nel 

 midollo degli uccelli, Memorie della Societa Toscana di Scienze Naturali. Vol. 

 X, Pisa, 1889. 



" Kolliker, a. — Ueber einen noch unbekannten Nervenzellenkern in Riick- 

 enmark der Vogel, Akad. Anzeiger (Wien), Nr. XXV, 1901. b.— Weitere Beo- 

 bachtungen iiber die Hofmann'schen Kerne am Mark der Vogel, Anatom. 

 Anzeiger, Bd. XXI, Nr. 3, 1902. c— L. c. 



