Fisher K R, Partlow G D, Walker A F
Anat Rec. 1986 Apr;214(4):432-40. doi: 10.1002/ar.1092140415.
The clinical and anatomical features of a live-born diprosopic lamb are described. There are no complete anatomical analyses of two-faced lambs in the literature despite the frequency of conjoined twinning in sheep. The lamb had two heads fused in the occipital region. Each head had two eyes. The pinnae of the medial ears were fused. Caudal to the neck the lamb appeared grossly normal. The lamb was unable to raise its heads or stand. Both heads showed synchronous sucking motions and cranial reflexes were present. Nystagmus, strabismus, and limb incoordination were present. The respiratory and heart rates were elevated. There was a grade IV murmur over the left heart base and a palpable thrill on the left side. Each head possessed a normal nasopharynx, oropharynx, and tongue. There was a singular laryngopharnyx and esophagus although the hyoid apparatus was partially duplicated. The cranial and cervical musculature reflected the head duplications. The aortic trunk emerged from the right ventricle just to the right of the conus arteriosus. A ventricular septal defect, patent foramen ovale, and ductus arteriosus were present along with malformed atrioventricular valves. Brainstem fusion began at the cranial medulla oblongata between cranial nerves IX and XII. The cerebella were separate but small. The ventromedial structures from each medulla oblongata were compressed into an extraneous midline remnant of tissue which extended caudally to the level of T2. The clinical signs therefore reflected the anatomical anomalies. A possible etiology for this diprosopus might be the presence early in development of an excessively large block of chordamesoderm. This would allow for the formation of two head folds and hence two "heads."
本文描述了一只活产双面羔羊的临床和解剖特征。尽管绵羊联体双胎的发生率较高，但文献中尚无对双面羔羊的完整解剖分析。这只羔羊的两个头部在枕部融合。每个头部有两只眼睛。内侧耳朵的耳廓融合。在颈部下方，羔羊外观大体正常。羔羊无法抬头或站立。两个头部均表现出同步吸吮动作，且存在颅反射。存在眼球震颤、斜视和肢体不协调。呼吸和心率加快。左心基部可闻及IV级杂音，左侧可触及震颤。每个头部都有正常的鼻咽、口咽和舌头。虽然舌骨装置部分重复，但有一个单一的喉咽和食管。头部和颈部肌肉组织反映了头部的重复情况。主动脉干从右心室发出，位于动脉圆锥右侧。存在室间隔缺损、卵圆孔未闭和动脉导管未闭，以及畸形的房室瓣。脑干融合始于颅神经IX和XII之间的延髓。小脑是分开的但较小。每个延髓的腹内侧结构被压缩成一个多余的中线组织残余，该残余向尾端延伸至T2水平。因此，临床症状反映了解剖学异常。这种双面畸形的一个可能病因可能是在发育早期存在一块过大的脊索中胚层。这将允许形成两个头褶，从而形成两个“头”。
