144 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



lear, nerve emerges from the dorsal aspect of the brain, at the posterior 

 boundary of the mesencephalon, and innervates the dorsal oblique 

 muscle. The sixth, or abducent, nerve takes its origin from the ventral 

 side of the metencephalon, and passes to the posterior rectus muscle. 

 A slender branch of this nerve is given off to the muscles of the nicti- 

 tating membrane (quadratus and pyramidalis). In Bronn's Thierreich 

 is mentioned on the authority of Bonsdorff an anastomosis between the 

 sixth nerve and the ramus ciliaris trigemini in Corvus cornix. In this 

 bird fibres are also said to pass to the ramus ciliaris externus of the cili- 

 ary ganglion ; while in Grus cinerea a fine branch of the abducens passes 

 partly to the ramus ciliaris interims of the ciliary ganglion, and partly 

 to the ganglion itself. The distribution of abducent fibres to the eyeball 

 in birds has also been recorded by Jegorow ('86-87), who considers it 

 possible that these may be sympathetic fibres, which join with the sixth 

 nerve as it passes through the cavernous sinus and proceed cephalad in 

 its trunk. 



2. Ciliary Ganglion. 



A well-marked ganglion is always found in connection with the oculo- 

 motor nerve of birds. This ganglion corresponds to the ciliary ganglion 

 of human anatomy, which was first described by Schacher in 1701 

 (Jegorow, '86-87). In man it occurs in the posterior region of the orbit- 

 as a small, laterally compressed, somewhat four-sided body, measuring 

 about 2 mm. in an antero-posterior direction. From behind it receives 

 branches from three different sources: a short or motor root (radix bre- 

 vis) from the oculomotor nerve, a long or sensory root (radix longa) from 

 the nasal branch of the ophthalmic division of the trigeminus, and a 

 sympathetic root (radix sympathica) from the sympathetic plexus of the 

 cavernous sinus. It gives off in front six to eight ciliary nerves, which 

 proceed to the sclerotic and choroid coats, ciliary muscle, iris and cornea 

 of the eyeball. These nerves are distinguished as the short ciliary 

 nerves from the so-called long ciliary nerves, which emanate from the 

 nasal branch of the trigeminus, and have the same distribution as the 

 short ciliaries (Quain's Anatomy, Thane, '95). 



The ganglion in question has received various names from different 

 authors (ciliary, ophthalmic, lenticular, oculomotor, Schacher's). It is 

 commonly described in the text-books of human anatomy in connection 

 with the trigeminal nerve. It is almost invariably stated to be sympa- 

 thetic in nature (as first suggested by Arnold, '31), although it differs 

 from typical sympathetic ganglia in giving origin to medullated periph- 

 eral nerves (the short ciliaries) instead of non-medullated fibres. 



