. Chordate morphology. Morphology (Animals); Chordata. velar valve first afferent branchial opening Q islet tissue Figure 9-26. Sagittal section through the head region of a lamprey. 9-28). The gall bladder lies between these lobes, and its short duct extends forward to enter the intestine slightly to the left of the midline and well behind the union of the pharynx and gut. At the point where the bile duct enters the gut, there is a swelling marking the mass of islet tissue of the pancreas. There is no spleen in either Myxine or Peiromyzon, although the latter has much lymphoid tissue in the t
. Chordate morphology. Morphology (Animals); Chordata. velar valve first afferent branchial opening Q islet tissue Figure 9-26. Sagittal section through the head region of a lamprey. 9-28). The gall bladder lies between these lobes, and its short duct extends forward to enter the intestine slightly to the left of the midline and well behind the union of the pharynx and gut. At the point where the bile duct enters the gut, there is a swelling marking the mass of islet tissue of the pancreas. There is no spleen in either Myxine or Peiromyzon, although the latter has much lymphoid tissue in the typhlosole of the larva. The myxinoid has myeloid tissue in the submucosa of the gut, while the adult lamprey, on the way to spawn, has some cell production going on in the blood itself and in the kidney tissue. The development of the is not well known. The telolecithal egg develops much as in the shark or teleost (Figure 7-14). Development is direct, without metamorphosis. General observations on fishes The abdominal viscera of fishes show the same basic pat- tern as the tetrapod both in terms of adult parts and in the developmental stages of these parts. The diffuse pancreas of the actinopterygian and the internal pancreas of the dipnoan or cyclostome raise the question of the primitive condition. The fact that the shark, or holocephalan, and Latimeria have a well-developed pancreas suggests that this was the original tentacles palatine commissure nasal tube cartilages nasal capsule olfactory fold in olfactory chamber frenulum of velu. nosohypophysea opening subnasal cartilage ethmoid tooth anterior lingual cartilage dentigerous cartilage'' / protrbctor muscle of dental plate / \ retractor muscle of dental plate medial lingual cartilage ligament of retractor muscle posterior lingual cartilage Figure 9-27. Sagittal section through the head region of Myx'me. 278 THE VISCERA. Please note that these images are extracted from scanned page images that may have been digital
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