34 H. LISSER 



THE NERVES 



The n. laryngeus superior can be traced to the vicinity of the 

 greater cornu of the hyoid, and the wing of the thyreoid, but I 

 could not follow either the motor branch to its inervation of the 

 crico thyreoideus muscle, or the sensorj^ portion, within the larynx. 

 Bits of tissue, were seen that might be nerve tissue, but I cannot 

 be certain of this branch of the vagus any further than to its prox- 

 imity to the hj^oid and thyreoid. The nerve Recurrens, later the 

 nerve laryngeus inferior (fig. 1) is better developed and can be 

 followed clearly to its innervation of the crico artyaenoideus pos- 

 terior ; but I cannot trace it to the other muscles, nor to any anas- 

 tomosis with the n. laryngeus superior. 



Embryo 317 — 12.5 mm. Frontal sections — 50ix 



THE CARTILAGES 



The thyreoid cartilage still consists purely of precartilage, — con- 

 densed mesenchyma, and has not changed greatly in appearance 

 from the one in the 10.5 mm. human embryo. However, rudi- 

 ments of a superior cornu and inferior cornu are just discernable, 

 and the lateral halves are not quite so rounded as a part of the 

 horseshoe arrangement, but rather more vertical as in fig. 3. The 

 ventral condensation is again in perfect continuity with the lateral 

 parts. This ventral portion is at a lower level than in the adult, 

 coming in close contact with the body of the cricoid, especially 

 its anterior arcus. The lateral wings are well removed from the 

 lateral portions of the cricoid, and between them is ample room for 

 the lateral larynx muscles; the circothyreoideus, circoarytaenoid- 

 eus lateralis, and perhaps thyreoarytaenoideus. 



The cricoid cartilage consists likewise of condensed mesenchyma 

 but is somewhat ahead of the thyreoid in assuming definite shape; 

 certainly the intensity of the condensation is greater, as deter- 

 mined by deeper staining and clearer outline; the ventral arcus 

 maintains its lead over the dorsal and lateral portions although 

 the latter show definite increase in the size of the condensed masses 



