DEVELOPMENT OF THE SKULL OF EMYS 715 



end of the cavum recessus utriculi. The canaUs semicircularis 

 anterior opens into it from above by the orificium inferius canaHs 

 semicircularis anterioris. The cavum ampullare anterius is differ- 

 entiated from that of the recessus utricuh which hes behind it 

 by a broad vertical ridge on the lateral capsular wall. 



The cavum utriculi, which occupies the middle portion of the 

 cavum vestibuli, is continuous dorsally with that of the sinus 

 superior utriculi, anteriorly with the recessus utriculi and ampulla 

 lateralis, posteriorly with the ampulla posterior and canalis semi- 

 circularis lateralis, and ventrally with the cavum sacculi. Its 

 median wall is formed throughout by the median capsular wall; 

 laterally it is bounded by the septum semicirculare laterale and, 

 ventral to the septum, by the lateral wall of the capsule which 

 is continuous with it. Anterior to the septum the cavity opens 

 laterally into the lateral ampulla and the recessus utriculi, and 

 posterior to the septum it is continuous with the median limb 

 of the lateral semicircular canal. At its anterior end the cavum 

 utriculi widens abruptly in a lateral direction to form the cavum 

 recessus utriculi, which lies rather ventral to the lateral ampulla. 



The cavum sinus superioris utriculi extends dorsally from the 

 cavum utriculi between the septa semicircularia anterius and 

 posterius. Opening into it from the anterior and lateral aspect 

 are the cava recessus utriculi and ampullare laterale. Dorsally 

 it opens into the orificia superioria canalis semicircularis anterioris 

 and posterioris. Medially and laterally it is limited by the respec- 

 tive capsular walls. 



The cavum recessus utriculi forms a pocket extending ven- 

 trally from the cavum ampullare laterale and anterior to the 

 cavum utriculi. Anteriorly it opens into the cavum ampullare 

 anterius and ventrally into that of the sacculus, but at its extreme 

 anterior end the ventral capsular wall limits it. 



The canalis semicircularis posterior curves laterally and ven- 

 trally from its union with the sinus superior utriculi, in a poste- 

 rior direction to the posterior ampulla, into which it opens from 

 above by means of the orificium inferius canalis semicircularis 

 posterioris. The canalis semicircularis lateralis connects with the 

 posterior portion of the posterior semicircular canal by means of 



