The pseudobranchial circulation in Amia calva. 129 



brancliial arch. Dorsally this anterior current passes along the ven- 

 tral surface of the but slightly developed pseudobranch, thus having 

 relations to that organ. The second, and still venous current passes, 

 in 12 mm embryos, through a capiHary network similar to that de- 

 scribed by FiiiEDRiCH MÜLLER iu 16 mm and 26 mm embryos of 

 Lepidosteus osseus; and the third current, if it still exists, is also 

 through a capillary network. The one or two posterior currents unite 

 dorsally, through the cross bar connection of earlier stages, with the 

 anterior current, this cross bar thus seeming to be the exact homo- 

 logue of the vessel formed by the union of the same currents in 

 16 mm and 26 mm embryos of Lepidosteus. Müller considers that 

 this cross bar in Lepidosteus is formed of two different parts or 

 components , a so-called "Querast" and an "Anastomose". It is 

 certainly not formed of two parts of different origin in Amia, and 

 I can not see, from Müller's descriptions , why it should be con- 

 sidered as so formed in Lepidosteus. 



In Selachian embryos of a certain age there are, according to 

 DoHRN (2), both afferent and efferent vessels in the hyoid arch, 

 the efferent vessel being connected by a cross commissure with an 

 anterior aortic vessel called by Dohrn the arteria thyreoidea man- 

 dibularis. This anterior aortic vessel is said to arise from the base 

 of the afferent artery of the hyoid arch, and to lie, at that point 

 and immediately beyond if, in close relations to the thyroid gland. 

 Of it Dohrn says (p. 7) : "Nicht weit von ihrem Ursprünge begegnet 

 sie allerhand Bluträumen, mit denen sie, wie es scheint, gemein- 

 same Sache macht, d. h. die Blutmassen , die immerhin nicht allzu 

 beträchtlich sind, verlaufen mit der Arteria thyreoidea im weitern 

 Verfolg gemeinsam, und es wird aus ihnen zusammen ein beträcht- 

 licheres Gefäss, welches neben und vor einem Nerven verläuft, einem 

 Ast des Facialis." Considerably beyond the thyroid gland this ar- 

 tery is joined by the commissure from the efferent artery of 

 the hyoid arch and then becomes the afferent artery of the spira- 

 cular gill. 



Dorsal to the cross-commissural bar the efferent artery of the 

 hyoid arch is said to turn inward along the hind edge of the hyo- 

 mandibular, and then forward and upward, to join a vessel that is 

 called by Dohrn the first aortic arch, and that is certainly the 

 homologue of the common carotid artery of my descriptions of Amia. 

 Anterior to the point where this carotid artery is joined by the 



Zool. Jahrb. AlV. Abth. 1. Morph. O 



