DEVELOPMENT OF THE HUMAN LARYNX 47 



tion of the muscles. But that a continuous muscle band, which 

 cannot be differentiated into individual muscles, exists at this stage 

 is not in accord with the results shown, especially in fig. 12, a 

 reconstruction of the 16 mm. stage, and in figs. 2, 8, 9, faithful 

 drawings of the sections of the 14 mm. embryo, and fig. 15 of the 

 16 mm. embryo. 



The cricothyreoideus, the cricoarytaenoideus posterior, and the 

 interarytaenoideus are definitely isolated, while the cricoarytaenoid- 

 eus lateralis and thyreoarytaenoideus are clearly separated from the 

 others aiid are about as much separated from each other as they 

 are in the adult. There is no need of describing them any further. 

 The figures show them all in sufficient detail. 



The constrictor muscles of the pharynx and oesophagus have 

 been reconstructed and the middle and inferior constrictors stand 

 out rather clearly. Nicolas states that the pharynx musculature 

 only unites from two independent lateral halves at 3 cm. I have 

 found perfect continuity at 10.5 mm. in the lower pharyngeal 

 portion, more union at 12.5 mm. and complete union at 14 nun. 



Several of the tongue and pharynx muscles have been included 

 in the illustrations, and it will be seen that they are very clearly 

 isolated and well developed even at the 14 mm. stage (figs. 7-9). 



For the identity of these muscles, I am under obligations to Dr. 

 Lewis, who very kindly gave me his own sketches, from which 

 figs. 7, 8 and 9 were developed. 



THE NERVES 



The nerves, are reconstructed in fig. 14 and in addition to show- 

 ing the superior laryngeus and n. recurrens and n. laryngeus 

 inferior, which can be followed to their respective innervations 

 and to their anastomosis, there is included the relations of these, 

 to the glossopharyngeal and to the hypoglossus (also figs. 15, 16, 

 19, 20). 



Embryo 22 — 20 mm. Transverse sections 



Embryo 22 measures 20 mm. V. B. and 18 mm. N. B., about 

 1h weeks old. 



