426 Proceedings of tJie Royal Irish Academy. 



XXXYIII. — Notes ox soiie Ai^roirAxiEs ik the cotirse of Xeetes en 



MAif. By AxEXANDEE Macalistee, M.B., Professor of Zoology and 



Comparative Anatomy, Dublin University, M.E.I. A. 

 [Eead November 8, 1875.] 

 The following are some varieties which I have noticed in the course 

 of nerves, in the Dissecting Eoom of the TJniversity of Dublin. 



1st. In a thin middle-aged female subject, a nerve, about as large 

 as the buccal, arose from the temporo-auricular, after the union of 

 the two roots of that trunk, it then passed over the internal maxillary 

 artery (which was normal) and was joined by a small twig which 

 arose fi'om the inferior dental nerve, dii'ectly below the foramen ovale 

 (thus making a loop around the artery). The trunk so formed de- 

 scended anterior to the usual inferior dental trunk, and pierced the 

 mandible at a point on the inner side of the bone opposite the mental 

 foramen, entered the inferior dental canal and supplied the incisor 

 teeth. The normal inferior dental nerve was smaller than usual, and 

 lay posterior to this anomalous trunk, from which it was separated by 

 the internal maxillary artery ; the mental nerve was large, and was 

 the terminal branch of the inferior dental, all the filaments of that 

 nerve leaving the inferior dental canal at this point. 



Cruveilhier and Sappey describe a fine anastomosis between the 

 auriculo-temporal and the inferior dental, but I am not aware of this 

 variety of that union having been previously observed. 



2nd. In a female subject the hypoglossal nerve, about half-an-inch 

 internal to its thyro-hyoid branch, gave off a transverse branch of 

 communication to its fellow of the opposite side ; this medial branch 

 arose below the twig for the genio-hyoicl, and passed superficial to that 

 muscle and under the mylo-hyoid ; in size the communicating trunk 

 was nearly equal to the continued trunk of that nerve. 



Communications between the hypoglossals of the two sides are on 

 record thus: Szabadfoldy (Yirchow's Ai'chiv. Band 38, s. 177) saw 

 twigs of the hypoglossus of one side passing through the septum of 

 the tongue to the opposite side ; Bach (Annotationes Anatomicse de 

 nervis hypoglosso et laryngeis : Turici, 1834, p. 10) noticed a sling- 

 like union of the two hypoglossi in the tip of the tongue, and my 

 case seems to be a variety, on a lower level and large scale, of that 

 method of union. 



3rd. The last specimen to which I will at present allude is one of 

 not very uncommon occurrence. In a female subject the phrenic 

 nerve arose as usual by a large root from the fourth cervical nerve (its 

 main root as shown by Luschka and others), but its usual accessory 

 branch from the fifth came off rather larger than usual, and lower 

 down than usual from its parent trunk ; it then ran down parallel to 

 the main root but 0-5" behind it, under the subclavian vein, and the 

 transversalis humeri and colli arteries, passed outside the internal mam- 

 mary, then across it, and joined the other portion of the phi'enic at the 

 level of the upper edge of the first rib. Yarieties in the position of 

 these two roots and in their place of union are not uncommon, bxxt 

 I have never seen so low a union before. 



