Lewis, Mixed Cerebral Nerves. 1 8 1 



A somatic sensory branch leaves the vagus just below its jugular 

 ganglion to supply the external acoustic meatus and the back part 

 of the auricle. This is the auricular branch of the vagus, which 

 may be joined by a similar branch from the glossopharyngeus. 



That the acoustic nerve should be considered a highly developed 

 special somatic portion of the intermedins, with which it is closely 

 connected in mammalian embryos, is regarded as probable by 

 some authorities. The entire separation of the acoustic elements 

 from the other cerebral nerves, as recorded by Worthington 

 (loc. cit., p. 170) in Bdellostoma is considered unique, and not 

 fundamental. 



All of the nerves and branches to which reference has been made 

 are shown in the following reconstruction (Plate XVII) of the 12 

 mm. pig, a revision of that published in the American Journal of 

 Anatomy, 1 903, vol. 2, following p. 225. In the new figure the 

 superior ganghon is more definitely outlined, and the large super- 

 ficial petrosal, the tympanic and the auricular nerves have been 

 added. The lettering is more consistent and complete. 



EXPLANATION OF PLATE XVII. 



Reconstruction of the brain ami cerebral nerves in a 12 mm. pig embryo. 



Nerves. — J, Oculomotor. 4, Trochlear. 5, Trigeminal, with its semilunar ganglion, s-l., 

 and three branches — oph., ophthalmic; mx., maxillary; md., mandibular. The motor portion which 

 goes with the mandibular nerve is concealed in this view by the sensory portion. 6, Abducens. 7, 

 Geniculate ganglion of the intermedins. Fibers from this ganglion mix with the motor fibers of the 

 facial portion, and both sorts enter the three branches — l.s.p., large superficial petrosal; ch.ty., chorda 

 tympani; ja., facial. 8, Acoustic, showing an upper vestibular portion, and a lower cochlear portion. 

 g, Glossopharyngeal, showing its superior ganglion, s, above; its petrosal ganglion, p., below; and 

 its three branches, — ty., tympanic; l.r., lingual ramus; ph.r., pharyngeal ramus. 10, Vagus, with 

 its jugular ganglion, j., extending posteriorly as a ganglionic commissure, com. Just below the jugular 

 ganglion the auricular branch extends forward. Below this is the ganglion nodosum, n. The branches 

 of the vagus here form the laryngeal plexus, with the superior laryngeal nerve above, and the recurrent 

 nerve, rec, below. //, Accessory portion of the vagus; ex., its ramus externus. 12, Hypoglossal. 

 F., Froriep's hypoglossal ganglion, c.i, c.2, c.J, Cervical nerves. 



Brain and Sense Organs. — Telen., Telencephalon. Dien., Diencephalon. Mes., Mesencephalon. 

 Meten., Metencephalon. Mye'en., Myelencephalon. H., Hemisphere. Ven. IV, Roof of the fourth 

 ventricle. Op., Optic cup. L., Lens. Na., Nasal pit. Ot., Otocyst. 



